Ihosvany Camps | Universidade Federal de Alfenas. Unifal-MG (original) (raw)
Papers by Ihosvany Camps
Proceedings of MOL2NET, International Conference on Multidisciplinary Sciences, 2015
Solid State Communications, 2005
The aim of this work is to study the dynamic formation and dissociation of trions and excitons in... more The aim of this work is to study the dynamic formation and dissociation of trions and excitons in double barrier resonant tunneling diodes. We propose a system of rate equations that takes into account the formation, dissociation and annihilation of these complexes inside the quantum well. From the solutions of the coupled equations, we are able to study the modulation of excitons and trions formation in the device as a function of the applied bias. The results of our model agree qualitatively with the experiments showing the viability of these rate equations system to study the dynamics of complex systems. q
Journal of medicinal plant research
This article reports the three biflavonoids isolated from the fruit pericarp of Garcinia brasilie... more This article reports the three biflavonoids isolated from the fruit pericarp of Garcinia brasiliensis Mart. (Clusiaceae): Morelloflavone-4```-glycoside (compound 1), (±)-Fukugiside (compound 2), and Morelloflavone (compound 3). Structural modifications by acylation and alkylation reactions were performed on the natural biflavonoid (±) morelloflavone to obtain three semisynthetic compounds: Morelloflavone-7,4`,7``,3```,4```-penta-O-acetyl (compound 4), Morelloflavone-7,4`,7``,3```,4```-penta-Omethyl (compound 5), and Morelloflavone-7,4`,7``,3```,4```-penta-O-butanoyl (compound 6). The inhibitory effects of these naturally isolated biflavonoid-type compounds and three semisynthetic derivatives on the activity of the cysteine proteases papain and cruzain, and on the serine protease trypsin were investigated. The potential inhibitory IC 50 of natural bioflavonoids compounds 1, 2, and 3 were 11.0 ± 3.0, 23.0 ± 4.0, and 10.5 ± 0.3 µM, respectively, for papain; 0.86 ± 0.12, 106 ± 7, and 3.8 ± 0.1, 50 ± 2, 119.5 ± 5, and 9.6 ± 1.0 µM, respectively, for cruzain. On the other hand, the semisynthetic biflavonoids compounds 4, 5, and 6 were more efficient in the inhibition of enzyme activity with IC 50 values 0.60 ± 0.02 µM (papain) for biflavonoids compound 4, 1.64 ± 0.11 µM (trypsin) for biflavonoids compound 5, and 8.1 ± 0.6 µM (cruzain) for biflavonoids compound 6. Compound 4 is more active owing to the carbonyl group in the structure; perhaps, this modification could favor a higher nucleophilic attack by serine and cysteine proteases. However, the semisynthetic compound 5 (IC 50 = 15.4 ± 0.7 µM for papain), which has no carbonyl group in structure, was less active in the inhibition. Interestingly, structure-activity relationships (SARs) were confirmed by flexible docking simulations. Likewise, the potential usefulness of natural compound 1 as an antioxidant compound was strengthened by our results concerning the antiproteolytic activity.
We make an adaptation of laser modelling equations to describe the behavior of a phonon laser (sa... more We make an adaptation of laser modelling equations to describe the behavior of a phonon laser (saser). Our saser consists of an AlGaAs/GaAs double barrier heterostructure designed to generate an intense beam of transversal acoustic (T A) phonons. To study our system, we begin with a Hamiltonian that describes the decay of primary longitudinal optical phonons (LO 1 ) into secondary (LO 2 ) and T A (LO 1 → LO 2 + T A) and its inverse process (recombination). Using this Hamiltonian, a set of coupled equations of motion for the phonons is obtained. We also consider the interaction between the phonons and its reservoirs. These interactions are introduced in the equations of motion leading to a set of coupled Langevin equations. In order to obtain an expression to describe our saser we apply, in the Langevin equations, an adiabatic elimination of some variables of the subsystem. Following the method above we obtain the value of the injection threshold for the operation of our phonon laser. At this threshold occurs a phase transition from a disordered to a coherent state. It is shown that it is not necessary a big "optical" pumping to get a sasing region.
Physica B: Condensed Matter, 2002
To study the emission properties of an AlGaAs-GaAs phonon laser we develop a formalism similar to... more To study the emission properties of an AlGaAs-GaAs phonon laser we develop a formalism similar to that used to describe a laser. The device studied here consist of a double-barrier resonant tunneling diode tailored to generate an intense rate of primary LO 1 phonons. These phonons are confined in the well and they decay into a pair of secondary LO 2 and TA phonons. The TA phonons are generated by stimulated emission and they are partially reflected in the well walls. A combination of these two processes leads, for injection rates greater than the threshold, to the selection of a single phonon mode. Finally, the TA phonons escape through the barriers forming an intense coherent phonon beam. We start with a Hamiltonian that takes into account the electrons, the three phonon branches, the electron-phonon interaction and the phonon-phonon interaction. The last one is responsible for the TA phonon generation. From this Hamiltonian we get a set of five coupled Heisenberg-Langevin equations that are solved making an expansion in coherent states and doing the usual adiabatic approximation. The threshold for phonon lasing is calculated. The results show that it is not necessary to have a big pumping to get a single mode operation. This confirm our previous results obtained using rougher approximations. The phonon laser studied here has a very short wavelength. The mean free path of TA phonons is of the order of 2 mm. Therefore, it could be useful to perform acoustic nanoscopy and other applications. r
Microelectronics Journal
We have investigated p-doped GaAs-AlAs resonant tunneling devices with asymmetric barriers under ... more We have investigated p-doped GaAs-AlAs resonant tunneling devices with asymmetric barriers under optical excitation. Transport and photoluminescence measurements were performed under identical bias conditions as a function of the light excitation intensity. We have observed the development of additional peaks, induced by illumination, between the main light- and heavy-hole resonances in the current-voltage characteristics (I(V)). We describe the behavior of these photo-induced peaks under a magnetic field parallel to the current. We propose that the observed properties are related to resonant tunneling of photoinduced electrons and associated excitonic effects.
Semiconductor Science and Technology
Cu2ZnSn(S1 − xSex)4 (CZT(S, Se)) is emerging as a very credible alternative to CuIn1 − xGaxSe2 (C... more Cu2ZnSn(S1 − xSex)4 (CZT(S, Se)) is emerging as a very credible alternative to CuIn1 − xGaxSe2 (CIGS) as the absorber layer for thin film solar cells. The former compound has the important advantage of using abundant Zn and Sn instead of the expensive In and Ga. A better understanding of the properties of CZT(S, Se) is being sought through experimental and theoretical means. Thus far, however, very little is known about the fundamental properties of the CZT(S, Se) alloys. In this work, theoretical studies on the structural, elastic, electronic and optical properties of CZT(S, Se) alloys through first-principles calculations are reported. We use a density functional code (aimpro), along with the Padé parametrization for the local density approximation to the exchange correlation potential. For the alloying calculations we employed 64 atom supercells (approximately cubic) with a 2 × 2 × 2 k-point sampling set. These supercells possess a total of 32 chalcogen species and the CZTSexS1 −...
Crystal Growth & Design, 2015
Exploring the Ln/succinate system and the template effect in hydrothermal synthesis made it possi... more Exploring the Ln/succinate system and the template effect in hydrothermal synthesis made it possible to obtain [La 2 (Succ) 3 (H 2 O) 3 ]·2H 2 O and [Ln 2 (Succ) 3 (H 2 O) 2 ]
MRS Proceedings, 2004
We report theoretical and experimental observation of photoexcitated hole spin selection in GaAs/... more We report theoretical and experimental observation of photoexcitated hole spin selection in GaAs/GaAlAs n-i-n in resonant tunneling diodes. When subjected to magnetic and electric parallel …elds, the spin splitted hole levels leads to several peak structure in the transmissivity. These experimental results are interpreted as an evidence of tunneling transport through spin polarized hole levels of non-magnetic diodes.
Journal of Organic Chemistry Research, 2013
There are many in silico studies of molecular systems whose tools help search for new molecules w... more There are many in silico studies of molecular systems whose tools help search for new molecules with biological activity. The aim of this work is to present a comparative study made using two different modeling tools in the study of interactions and complex formation between Cathepsin G and morelloflavone. The first modeling tool used was molecular docking using the genetic algorithm methodology. The second tool was the semi-empirical method for structure optimizations in vacuum and in the presence of a solvent. The results shown that the optimized Cathepsin G-morelloflavone complex had a better affinity (30%) than the complex obtained from the docking process. This demonstrates the importance of using methods that consider the electronic structure and solvent effects on the formation of protein-inhibitor complexes.
Solid State Communications, 2000
We make an adaptation of laser modeling equations to describe the behavior of a phonon laser (sas... more We make an adaptation of laser modeling equations to describe the behavior of a phonon laser (saser). Our saser consists of an AlGaAs/GaAs double barrier heterostructure designed to generate an intense beam of transversal acoustic (TA) phonons. To study our system, we begin with a Hamiltonian that describes the decay of primary longitudinal optical phonons (LO 1 ) into secondary (LO 2 ) and TA (LO 1 3 LO 2 ϩ TA) and its inverse process (recombination). Using this Hamiltonian, a set of coupled equations of motion for the phonons is obtained. We also consider the interaction between the phonons and its reservoirs. These interactions are introduced in the equations of motion leading to a set of coupled Langevin equations. In order to obtain an expression to describe our saser, we apply, in the Langevin equations, an adiabatic elimination of some variables of the subsystem. Following the method above we obtain the value of the injection threshold for the operation of our phonon laser. At this threshold occurs a phase transition from a disordered to a coherent state. It is shown that a big "optical" pumping is not necessary to get a sasing region. ᭧
Semiconductor Science and Technology, 2006
In this paper, we report on the effects of the environment on the properties of an ensemble of In... more In this paper, we report on the effects of the environment on the properties of an ensemble of InAs self-assembled quantum dots. The properties presented by the electrons confined at the dots can be tuned by adjusting some parameters of the environment. Using capacitance-voltage and photoluminescence measurements, we observed an increase in the thermal stability of zero-dimensional electron gas when the dots were grown in a period of a GaAs/AlAs superlattice. We believe that the parameter responsible for the thermal stability observed here was the increase of the electrical impedance of the device. In addition, electrical and optical measurements enabled us to study the thermal stability of electrons located at the dots grown in the GaAs bulk and in the aforementioned superlattice.
Semiconductor Science and Technology, 2002
In this work, we analysed the cavity length dependence of the internal, differential and power co... more In this work, we analysed the cavity length dependence of the internal, differential and power conversion efficiencies in AlGaAs/GaAs multiquantum well (MQW) lasers. We developed a theoretical model to calculate the threshold current and from it, the corresponding efficiencies. In this model we take into account a radiative process, and nonradiative mechanisms such as recombination from X and L valleys of the conduction band, Auger recombination, interface recombination and the carrier leakage over the heterostructure. Our modelling results for the threshold current are compared with the experimental data reported in the literature for different structures, showing a good agreement. We show that the internal and differential quantum efficiencies are greater in MQW lasers for all cavity lengths. In the case of the power conversion efficiency, it is higher only in MQW lasers than in their single quantum well counterparts for small values of cavity lengths.
Semiconductor Science and Technology, 2007
Confined polar optical phonons are studied in a semiconductor double heterostructure (SDH) by mea... more Confined polar optical phonons are studied in a semiconductor double heterostructure (SDH) by means of a generalization of a theory developed some years ago and based on a continuous medium model. The treatment considers the coupling of electro-mechanical oscillations and involves dispersive phonons. This approach has provided results beyond the usually applied dielectric continuum models, where just the electric aspect of the oscillations is analyzed. In the previous works on the subject the theory included phonon dispersion within a quadratic (parabolic) approximation, while presently linear contributions were added by a straightforward extension of the fundamental equations. The generalized version of the mentioned theoretical treatment leads to a description of long wavelength polar optical phonons showing a closer agreement with experimental data and with calculations along atomistic models. This is particularly important for systems where the linear contribution to dispersion becomes predominant. We present a systematic derivation of the underlying equations, their solutions for the bulk and SDH cases, providing us a complete description of the dispersive modes and the associated electron-phonon Hamiltonian. The results obtained are applied to the case of a EuS/PbS/EuS quantum-well.
Physical Review B, 2006
We have investigated polarization-resolved photoluminescence under applied voltage in p-i-p GaAs/... more We have investigated polarization-resolved photoluminescence under applied voltage in p-i-p GaAs/ AlAs double-barrier diodes. We have observed oscillations in the degree of polarization up to 36% at B = 15 T with sign reversals occurring near to the hole subband resonances. At high voltages a polarization saturation up to 25% at B = 15 T is observed. The data are interpreted by using simulations based on a simple theoretical model that considers spin conservation for tunneling and the relaxation processes for carriers at Zeeman states in the quantum well. Our work offers the prospect for the development of voltage-controlled spin filtering systems using standard nonmagnetic semiconductor heterostructures.
Physical Review B, 2006
We report experimental evidence of excitonic spin-splitting, in addition to the conventional Zeem... more We report experimental evidence of excitonic spin-splitting, in addition to the conventional Zeeman effect, produced by a combination of the Rashba spin-orbit interaction, Stark shift and charge screening. The electric-field-induced modulation of the spin-splitting are studied during the charging and discharging processes of p-type GaAs/AlAs double barrier resonant tunneling diodes (RTD) under applied bias and magnetic field. The abrupt changes in the photoluminescence, with the applied bias, provide information of the charge accumulation effects on the device.
Molecular Informatics, 2011
The cyclin-dependent kinases or CDKs participate in the regulation of both the cell progression c... more The cyclin-dependent kinases or CDKs participate in the regulation of both the cell progression cycle and the RNA polymerase-II transcription cycle. In several human tumours deregulation of CDK-related mechanisms have been detected, e.g., overexpression of cyclins or deletion of genes encoding for CKIs. Regarding these observations, CDKs came up to be interesting targets for elaboration of novel antitumour drugs. Based on the importance of the CDKs, this research aimed to describe, to characterize and to compare the molecular models of CDK1 and CDK3. Since the structures of human CDK1 and CDK3 are unavailable in the Protein Data Bank -PDB, homology models were created based on the CDK2 as the template, once they share a substantial identity. The structural studies of the CDK1 and CDK3 biding sites were conducted by molecular docking with 15 different CDK inhibitors previously identified to CDK2. This study allowed the understanding of the structure of the complexes between CDK1/ CDK3 with inhibitors. The knowledge of their structural features mainly the biding sites might be useful to discovery and rationalization of drug design process.
Microelectronics Journal, 2005
We have studied the effects of excitonic complexes formation, such as excitons and trions, on the... more We have studied the effects of excitonic complexes formation, such as excitons and trions, on the optical and on transport properties of GaAs-GaAlAs n-i-n double barrier diodes, by measuring the current-voltage characteristics and the photoluminescence emission, as function of bias. The observation of a pre-resonance shoulder in the I(V) curves, under high laser intensities, and a negative charged excitons in the photoluminescence spectra, under the same bias conditions, were associated to the dissociation of these complexes either by thermal excitation or by scattering with 'free' carriers in the quantum well layer. A simple rate equation model allows us to explain the kinetics of the excitonic complexes in double barrier devices. q
Materials Science and Engineering: B, 2004
We have investigated transport and optical properties in GaAs-Al 0.35 Ga 0.65 As double-barrier d... more We have investigated transport and optical properties in GaAs-Al 0.35 Ga 0.65 As double-barrier diodes. We have observed an unexpected enhancement of the integrated photoluminescence (PL) intensity and photocurrent (PC) with increasing temperature. For the integrated PL intensity, this enhancement is followed by an expected decrease at higher temperatures once effective nonradiative mechanisms become activated. The observed behavior in the photocurrent is associated to the dependence of hole mobility on the temperature. We have developed a model to fit the integrated PL intensity that combines the effects of the density of minority carriers (holes) generated at the contact and the dependence of hole mobility on the temperature. The minority carrier mobility is obtained from PC measurements. # 2004 Published by Elsevier B.V.
Journal of Molecular Modeling, 2014
The adsorption of Ni, Cd, and Pb on a zigzag (10, 0) carbon nanotube (CNT) surface was investigat... more The adsorption of Ni, Cd, and Pb on a zigzag (10, 0) carbon nanotube (CNT) surface was investigated using density functional theory. Binding energy calculations were performed, and the results indicated that the three metals are stably adsorbed on the nanotube surface. Moreover, the results showed that Cd is physisorbed whereas Ni and Pb are chemisorbed. Our studies show that the electronic properties of the CNT are modified by the chemisorption mechanism (Ni and Pb). After Ni and Pb adsorption, the nanotube changes from being a semiconductor to a metallic conductor. The nanotube remains semiconductive upon Cd physisorption, although a decrease in the band gap is observed. Also, Ni or Pb adsorption triggers a change in the magnetism of the nanotube through the induction of spin polarization. Not only can these results of our calculations be used to explain the adsorption mechanisms of these heavy metals on the CNT, but they are also useful for evaluating the potential of carbon nanotubes (CNTs) to act as filters and sensors of such metals.
Proceedings of MOL2NET, International Conference on Multidisciplinary Sciences, 2015
Solid State Communications, 2005
The aim of this work is to study the dynamic formation and dissociation of trions and excitons in... more The aim of this work is to study the dynamic formation and dissociation of trions and excitons in double barrier resonant tunneling diodes. We propose a system of rate equations that takes into account the formation, dissociation and annihilation of these complexes inside the quantum well. From the solutions of the coupled equations, we are able to study the modulation of excitons and trions formation in the device as a function of the applied bias. The results of our model agree qualitatively with the experiments showing the viability of these rate equations system to study the dynamics of complex systems. q
Journal of medicinal plant research
This article reports the three biflavonoids isolated from the fruit pericarp of Garcinia brasilie... more This article reports the three biflavonoids isolated from the fruit pericarp of Garcinia brasiliensis Mart. (Clusiaceae): Morelloflavone-4```-glycoside (compound 1), (±)-Fukugiside (compound 2), and Morelloflavone (compound 3). Structural modifications by acylation and alkylation reactions were performed on the natural biflavonoid (±) morelloflavone to obtain three semisynthetic compounds: Morelloflavone-7,4`,7``,3```,4```-penta-O-acetyl (compound 4), Morelloflavone-7,4`,7``,3```,4```-penta-Omethyl (compound 5), and Morelloflavone-7,4`,7``,3```,4```-penta-O-butanoyl (compound 6). The inhibitory effects of these naturally isolated biflavonoid-type compounds and three semisynthetic derivatives on the activity of the cysteine proteases papain and cruzain, and on the serine protease trypsin were investigated. The potential inhibitory IC 50 of natural bioflavonoids compounds 1, 2, and 3 were 11.0 ± 3.0, 23.0 ± 4.0, and 10.5 ± 0.3 µM, respectively, for papain; 0.86 ± 0.12, 106 ± 7, and 3.8 ± 0.1, 50 ± 2, 119.5 ± 5, and 9.6 ± 1.0 µM, respectively, for cruzain. On the other hand, the semisynthetic biflavonoids compounds 4, 5, and 6 were more efficient in the inhibition of enzyme activity with IC 50 values 0.60 ± 0.02 µM (papain) for biflavonoids compound 4, 1.64 ± 0.11 µM (trypsin) for biflavonoids compound 5, and 8.1 ± 0.6 µM (cruzain) for biflavonoids compound 6. Compound 4 is more active owing to the carbonyl group in the structure; perhaps, this modification could favor a higher nucleophilic attack by serine and cysteine proteases. However, the semisynthetic compound 5 (IC 50 = 15.4 ± 0.7 µM for papain), which has no carbonyl group in structure, was less active in the inhibition. Interestingly, structure-activity relationships (SARs) were confirmed by flexible docking simulations. Likewise, the potential usefulness of natural compound 1 as an antioxidant compound was strengthened by our results concerning the antiproteolytic activity.
We make an adaptation of laser modelling equations to describe the behavior of a phonon laser (sa... more We make an adaptation of laser modelling equations to describe the behavior of a phonon laser (saser). Our saser consists of an AlGaAs/GaAs double barrier heterostructure designed to generate an intense beam of transversal acoustic (T A) phonons. To study our system, we begin with a Hamiltonian that describes the decay of primary longitudinal optical phonons (LO 1 ) into secondary (LO 2 ) and T A (LO 1 → LO 2 + T A) and its inverse process (recombination). Using this Hamiltonian, a set of coupled equations of motion for the phonons is obtained. We also consider the interaction between the phonons and its reservoirs. These interactions are introduced in the equations of motion leading to a set of coupled Langevin equations. In order to obtain an expression to describe our saser we apply, in the Langevin equations, an adiabatic elimination of some variables of the subsystem. Following the method above we obtain the value of the injection threshold for the operation of our phonon laser. At this threshold occurs a phase transition from a disordered to a coherent state. It is shown that it is not necessary a big "optical" pumping to get a sasing region.
Physica B: Condensed Matter, 2002
To study the emission properties of an AlGaAs-GaAs phonon laser we develop a formalism similar to... more To study the emission properties of an AlGaAs-GaAs phonon laser we develop a formalism similar to that used to describe a laser. The device studied here consist of a double-barrier resonant tunneling diode tailored to generate an intense rate of primary LO 1 phonons. These phonons are confined in the well and they decay into a pair of secondary LO 2 and TA phonons. The TA phonons are generated by stimulated emission and they are partially reflected in the well walls. A combination of these two processes leads, for injection rates greater than the threshold, to the selection of a single phonon mode. Finally, the TA phonons escape through the barriers forming an intense coherent phonon beam. We start with a Hamiltonian that takes into account the electrons, the three phonon branches, the electron-phonon interaction and the phonon-phonon interaction. The last one is responsible for the TA phonon generation. From this Hamiltonian we get a set of five coupled Heisenberg-Langevin equations that are solved making an expansion in coherent states and doing the usual adiabatic approximation. The threshold for phonon lasing is calculated. The results show that it is not necessary to have a big pumping to get a single mode operation. This confirm our previous results obtained using rougher approximations. The phonon laser studied here has a very short wavelength. The mean free path of TA phonons is of the order of 2 mm. Therefore, it could be useful to perform acoustic nanoscopy and other applications. r
Microelectronics Journal
We have investigated p-doped GaAs-AlAs resonant tunneling devices with asymmetric barriers under ... more We have investigated p-doped GaAs-AlAs resonant tunneling devices with asymmetric barriers under optical excitation. Transport and photoluminescence measurements were performed under identical bias conditions as a function of the light excitation intensity. We have observed the development of additional peaks, induced by illumination, between the main light- and heavy-hole resonances in the current-voltage characteristics (I(V)). We describe the behavior of these photo-induced peaks under a magnetic field parallel to the current. We propose that the observed properties are related to resonant tunneling of photoinduced electrons and associated excitonic effects.
Semiconductor Science and Technology
Cu2ZnSn(S1 − xSex)4 (CZT(S, Se)) is emerging as a very credible alternative to CuIn1 − xGaxSe2 (C... more Cu2ZnSn(S1 − xSex)4 (CZT(S, Se)) is emerging as a very credible alternative to CuIn1 − xGaxSe2 (CIGS) as the absorber layer for thin film solar cells. The former compound has the important advantage of using abundant Zn and Sn instead of the expensive In and Ga. A better understanding of the properties of CZT(S, Se) is being sought through experimental and theoretical means. Thus far, however, very little is known about the fundamental properties of the CZT(S, Se) alloys. In this work, theoretical studies on the structural, elastic, electronic and optical properties of CZT(S, Se) alloys through first-principles calculations are reported. We use a density functional code (aimpro), along with the Padé parametrization for the local density approximation to the exchange correlation potential. For the alloying calculations we employed 64 atom supercells (approximately cubic) with a 2 × 2 × 2 k-point sampling set. These supercells possess a total of 32 chalcogen species and the CZTSexS1 −...
Crystal Growth & Design, 2015
Exploring the Ln/succinate system and the template effect in hydrothermal synthesis made it possi... more Exploring the Ln/succinate system and the template effect in hydrothermal synthesis made it possible to obtain [La 2 (Succ) 3 (H 2 O) 3 ]·2H 2 O and [Ln 2 (Succ) 3 (H 2 O) 2 ]
MRS Proceedings, 2004
We report theoretical and experimental observation of photoexcitated hole spin selection in GaAs/... more We report theoretical and experimental observation of photoexcitated hole spin selection in GaAs/GaAlAs n-i-n in resonant tunneling diodes. When subjected to magnetic and electric parallel …elds, the spin splitted hole levels leads to several peak structure in the transmissivity. These experimental results are interpreted as an evidence of tunneling transport through spin polarized hole levels of non-magnetic diodes.
Journal of Organic Chemistry Research, 2013
There are many in silico studies of molecular systems whose tools help search for new molecules w... more There are many in silico studies of molecular systems whose tools help search for new molecules with biological activity. The aim of this work is to present a comparative study made using two different modeling tools in the study of interactions and complex formation between Cathepsin G and morelloflavone. The first modeling tool used was molecular docking using the genetic algorithm methodology. The second tool was the semi-empirical method for structure optimizations in vacuum and in the presence of a solvent. The results shown that the optimized Cathepsin G-morelloflavone complex had a better affinity (30%) than the complex obtained from the docking process. This demonstrates the importance of using methods that consider the electronic structure and solvent effects on the formation of protein-inhibitor complexes.
Solid State Communications, 2000
We make an adaptation of laser modeling equations to describe the behavior of a phonon laser (sas... more We make an adaptation of laser modeling equations to describe the behavior of a phonon laser (saser). Our saser consists of an AlGaAs/GaAs double barrier heterostructure designed to generate an intense beam of transversal acoustic (TA) phonons. To study our system, we begin with a Hamiltonian that describes the decay of primary longitudinal optical phonons (LO 1 ) into secondary (LO 2 ) and TA (LO 1 3 LO 2 ϩ TA) and its inverse process (recombination). Using this Hamiltonian, a set of coupled equations of motion for the phonons is obtained. We also consider the interaction between the phonons and its reservoirs. These interactions are introduced in the equations of motion leading to a set of coupled Langevin equations. In order to obtain an expression to describe our saser, we apply, in the Langevin equations, an adiabatic elimination of some variables of the subsystem. Following the method above we obtain the value of the injection threshold for the operation of our phonon laser. At this threshold occurs a phase transition from a disordered to a coherent state. It is shown that a big "optical" pumping is not necessary to get a sasing region. ᭧
Semiconductor Science and Technology, 2006
In this paper, we report on the effects of the environment on the properties of an ensemble of In... more In this paper, we report on the effects of the environment on the properties of an ensemble of InAs self-assembled quantum dots. The properties presented by the electrons confined at the dots can be tuned by adjusting some parameters of the environment. Using capacitance-voltage and photoluminescence measurements, we observed an increase in the thermal stability of zero-dimensional electron gas when the dots were grown in a period of a GaAs/AlAs superlattice. We believe that the parameter responsible for the thermal stability observed here was the increase of the electrical impedance of the device. In addition, electrical and optical measurements enabled us to study the thermal stability of electrons located at the dots grown in the GaAs bulk and in the aforementioned superlattice.
Semiconductor Science and Technology, 2002
In this work, we analysed the cavity length dependence of the internal, differential and power co... more In this work, we analysed the cavity length dependence of the internal, differential and power conversion efficiencies in AlGaAs/GaAs multiquantum well (MQW) lasers. We developed a theoretical model to calculate the threshold current and from it, the corresponding efficiencies. In this model we take into account a radiative process, and nonradiative mechanisms such as recombination from X and L valleys of the conduction band, Auger recombination, interface recombination and the carrier leakage over the heterostructure. Our modelling results for the threshold current are compared with the experimental data reported in the literature for different structures, showing a good agreement. We show that the internal and differential quantum efficiencies are greater in MQW lasers for all cavity lengths. In the case of the power conversion efficiency, it is higher only in MQW lasers than in their single quantum well counterparts for small values of cavity lengths.
Semiconductor Science and Technology, 2007
Confined polar optical phonons are studied in a semiconductor double heterostructure (SDH) by mea... more Confined polar optical phonons are studied in a semiconductor double heterostructure (SDH) by means of a generalization of a theory developed some years ago and based on a continuous medium model. The treatment considers the coupling of electro-mechanical oscillations and involves dispersive phonons. This approach has provided results beyond the usually applied dielectric continuum models, where just the electric aspect of the oscillations is analyzed. In the previous works on the subject the theory included phonon dispersion within a quadratic (parabolic) approximation, while presently linear contributions were added by a straightforward extension of the fundamental equations. The generalized version of the mentioned theoretical treatment leads to a description of long wavelength polar optical phonons showing a closer agreement with experimental data and with calculations along atomistic models. This is particularly important for systems where the linear contribution to dispersion becomes predominant. We present a systematic derivation of the underlying equations, their solutions for the bulk and SDH cases, providing us a complete description of the dispersive modes and the associated electron-phonon Hamiltonian. The results obtained are applied to the case of a EuS/PbS/EuS quantum-well.
Physical Review B, 2006
We have investigated polarization-resolved photoluminescence under applied voltage in p-i-p GaAs/... more We have investigated polarization-resolved photoluminescence under applied voltage in p-i-p GaAs/ AlAs double-barrier diodes. We have observed oscillations in the degree of polarization up to 36% at B = 15 T with sign reversals occurring near to the hole subband resonances. At high voltages a polarization saturation up to 25% at B = 15 T is observed. The data are interpreted by using simulations based on a simple theoretical model that considers spin conservation for tunneling and the relaxation processes for carriers at Zeeman states in the quantum well. Our work offers the prospect for the development of voltage-controlled spin filtering systems using standard nonmagnetic semiconductor heterostructures.
Physical Review B, 2006
We report experimental evidence of excitonic spin-splitting, in addition to the conventional Zeem... more We report experimental evidence of excitonic spin-splitting, in addition to the conventional Zeeman effect, produced by a combination of the Rashba spin-orbit interaction, Stark shift and charge screening. The electric-field-induced modulation of the spin-splitting are studied during the charging and discharging processes of p-type GaAs/AlAs double barrier resonant tunneling diodes (RTD) under applied bias and magnetic field. The abrupt changes in the photoluminescence, with the applied bias, provide information of the charge accumulation effects on the device.
Molecular Informatics, 2011
The cyclin-dependent kinases or CDKs participate in the regulation of both the cell progression c... more The cyclin-dependent kinases or CDKs participate in the regulation of both the cell progression cycle and the RNA polymerase-II transcription cycle. In several human tumours deregulation of CDK-related mechanisms have been detected, e.g., overexpression of cyclins or deletion of genes encoding for CKIs. Regarding these observations, CDKs came up to be interesting targets for elaboration of novel antitumour drugs. Based on the importance of the CDKs, this research aimed to describe, to characterize and to compare the molecular models of CDK1 and CDK3. Since the structures of human CDK1 and CDK3 are unavailable in the Protein Data Bank -PDB, homology models were created based on the CDK2 as the template, once they share a substantial identity. The structural studies of the CDK1 and CDK3 biding sites were conducted by molecular docking with 15 different CDK inhibitors previously identified to CDK2. This study allowed the understanding of the structure of the complexes between CDK1/ CDK3 with inhibitors. The knowledge of their structural features mainly the biding sites might be useful to discovery and rationalization of drug design process.
Microelectronics Journal, 2005
We have studied the effects of excitonic complexes formation, such as excitons and trions, on the... more We have studied the effects of excitonic complexes formation, such as excitons and trions, on the optical and on transport properties of GaAs-GaAlAs n-i-n double barrier diodes, by measuring the current-voltage characteristics and the photoluminescence emission, as function of bias. The observation of a pre-resonance shoulder in the I(V) curves, under high laser intensities, and a negative charged excitons in the photoluminescence spectra, under the same bias conditions, were associated to the dissociation of these complexes either by thermal excitation or by scattering with 'free' carriers in the quantum well layer. A simple rate equation model allows us to explain the kinetics of the excitonic complexes in double barrier devices. q
Materials Science and Engineering: B, 2004
We have investigated transport and optical properties in GaAs-Al 0.35 Ga 0.65 As double-barrier d... more We have investigated transport and optical properties in GaAs-Al 0.35 Ga 0.65 As double-barrier diodes. We have observed an unexpected enhancement of the integrated photoluminescence (PL) intensity and photocurrent (PC) with increasing temperature. For the integrated PL intensity, this enhancement is followed by an expected decrease at higher temperatures once effective nonradiative mechanisms become activated. The observed behavior in the photocurrent is associated to the dependence of hole mobility on the temperature. We have developed a model to fit the integrated PL intensity that combines the effects of the density of minority carriers (holes) generated at the contact and the dependence of hole mobility on the temperature. The minority carrier mobility is obtained from PC measurements. # 2004 Published by Elsevier B.V.
Journal of Molecular Modeling, 2014
The adsorption of Ni, Cd, and Pb on a zigzag (10, 0) carbon nanotube (CNT) surface was investigat... more The adsorption of Ni, Cd, and Pb on a zigzag (10, 0) carbon nanotube (CNT) surface was investigated using density functional theory. Binding energy calculations were performed, and the results indicated that the three metals are stably adsorbed on the nanotube surface. Moreover, the results showed that Cd is physisorbed whereas Ni and Pb are chemisorbed. Our studies show that the electronic properties of the CNT are modified by the chemisorption mechanism (Ni and Pb). After Ni and Pb adsorption, the nanotube changes from being a semiconductor to a metallic conductor. The nanotube remains semiconductive upon Cd physisorption, although a decrease in the band gap is observed. Also, Ni or Pb adsorption triggers a change in the magnetism of the nanotube through the induction of spin polarization. Not only can these results of our calculations be used to explain the adsorption mechanisms of these heavy metals on the CNT, but they are also useful for evaluating the potential of carbon nanotubes (CNTs) to act as filters and sensors of such metals.