Humberto Cabrera | Instituto Venezolano de Investigaciones Cientificas - IVIC (original) (raw)

Papers by Humberto Cabrera

Journal of Clinical & Experimental Dermatology Research, 2015

Nevus spilus or speckled lentiginous nevus is a mixed nevus and presents as a light-brown macule ... more Nevus spilus or speckled lentiginous nevus is a mixed nevus and presents as a light-brown macule with macular and/or papular-nodular lesions scattered across it. When lateralized, they can be associated with other anomalies, particularly neurological and musculoskeletal becoming the nevus spilus syndrome. We report a 16-year-old boy with a giant segmental nevus spilus associated with congenital spondylolysis.

Review of Scientific Instruments

We report a highly stable and affordable dual-wavelength digital holographic microscopy system ba... more We report a highly stable and affordable dual-wavelength digital holographic microscopy system based on common-path geometry. A Fresnel biprism is used to create an off-axis geometry, and two diode laser sources with different wavelengths λ1 = 532 nm and λ2 = 650 nm generate the dual-wavelength compound hologram. In order to extend the measurement range, the phase distribution is obtained using a synthetic wavelength Λ1 = 2930.5 nm. Furthermore, to improve the system's temporal stability and reduce speckle noise, a shorter wavelength (Λ2 = 292.5 nm) is used. The feasibility of the proposed configuration is validated by the experimental results obtained with Molybdenum trioxide, Paramecium, and red blood cell specimens.

Photonics

The emergence of diversified applications of laser-induced breakdown spectroscopy in the biomedic... more The emergence of diversified applications of laser-induced breakdown spectroscopy in the biomedical field, electronics, space physics, and material processing necessitates a comprehensive understanding of plasma parameters. The present work delineates the structure and evolution of copper plasma under different ambient pressures (0.01 mbar to 100 mbar) along with other plasma parameters. The study reveals the role of ambient pressure in the increase of plasma temperature (Te), electron density (Ne), number of particles in the Debye sphere, plasma frequency, inverse bremsstrahlung absorption coefficient, electron thermal velocity, electron–ion collision frequency and in the decrease of Debye length (λD) and plasma skin depth (PSD). The experimental techniques and the theoretical explanations for the variation of plasma parameters and their applications are also detailed. As the ambient pressure increases, the motion of plasma species becomes restricted, resulting in the increase of T...

Acquiring morphological and photothermal information is essential for characterization of a varie... more Acquiring morphological and photothermal information is essential for characterization of a variety of samples in biochemistry, material science and process technologies. In this paper, we report on the integration of digital holographic microscopy (DHM) and thermal lens (TL) spectrometry techniques enabling simultaneous measurement of both class of properties: morphological images and photothermal parameters. DHM in transmission mode is an effective technique for label-free, non-contact, real-time, and non-invasive imaging and measurement of phase objects, such as biomaterials. On the other hand, TL is a highly sensitive methodology to detect low concentrations of analytes in low absorbing samples. We demonstrate the usefulness of the DHM-TL integrated system by applying it to obtain morphometrical information of samples as well as for acquisition of their photothermal maps. Further, by extending the concept of “microsphere-assisted (MS) imaging” into TL, we show that MS-TL enables...

Photonics

Charge carriers’ generation from zinc includes silicon quantum dots (ZnSiQDs) layer sandwiched in... more Charge carriers’ generation from zinc includes silicon quantum dots (ZnSiQDs) layer sandwiched in-between porous silicon (PSi) and titania nanoparticles (TiO2NPs) layer-based solar cell is an efficient way to improve the cell’s performance. In this view, ZnSiQDs layer with various QDs sizes have been inserted, separating the PSi and TiO2NPs layers to achieve some graded bandgap quantum dot solar cells (GBQDSCs). In this process, ZnSiQDs of mean diameter 1.22 nm is first prepared via the top-down method. Next, ZnSiQDs have been re-grown using the bottom-up approach to get various mean diameters of 2.1, 2.7 and 7.4 nm. TiO2NPs of mean diameter in the range of 3.2 to 33.94 nm have been achieved via thermal annealing. The influence of different ZnSiQDs sizes on the designed GBGQDSCs performance has been determined. The proposed cell attains a short circuit current of 40 mA/cm2 and an efficiency of 4.9%. It has been shown that the cell performance enhances by optimizing the energy levels...

Optics and Lasers in Engineering

Journal of Cancer Science & Therapy, Mar 25, 2014

Review of Scientific Instruments, 2018

Journal of Physics D: Applied Physics, 2015

We report on the measurement of the thermal diffusivity, D, of few-layers graphene obtained by ch... more We report on the measurement of the thermal diffusivity, D, of few-layers graphene obtained by chemical vapor deposition, using a noncontact optical microscopy method based on a mode mismatched thermal lens technique in a pump-probe two-laser beams configuration. It takes advantage of the coaxial counter propagating tightly focused excitation and collimated probe beams in an improved thermal lens microscopy setup. The obtained results: D = (6.5 ± 0.09) × 10−4 m2 s−1, D = (1.9 ± 0.07) × 10−4 m2 s−1 and D = (1.3 ± 0.05) × 10−4 m2 s−1 for four (on a glass slide), eight and sixteen graphene (freestanding) layers are reasonable values, as can be concluded from reported literature data.

Nanomaterials

Herein, we report on a smart biosensing platform that exploits gold nanoparticles (AuNPs) functio... more Herein, we report on a smart biosensing platform that exploits gold nanoparticles (AuNPs) functionalized through ssDNA self-assembled monolayers (SAM) and the DNA-directed immobilization (DDI) of DNA-protein conjugates; a novel, high-sensitivity optical characterization technique based on a miniaturized gel electrophoresis chip integrated with online thermal lens spectrometry (MGEC-TLS), for the high-sensitivity detection of antigen binding events. Specifically, we characterized the physicochemical properties of 20 nm AuNPs covered with mixed SAMs of thiolated single-stranded DNA and bio-repellent molecules, referred to as top-terminated oligo-ethylene glycol (TOEG6), demonstrating high colloidal stability, optimal binder surface density, and proper hybridization capacity. Further, to explore the design in the frame of cancer-associated antigen detection, complementary ssDNA fragments conjugated with a nanobody, called C8, were loaded on the particles and employed to detect the pres...

Applied Sciences

Co-doped Zinc selenide (ZnSe) is a promising material because of a high photoluminescence efficie... more Co-doped Zinc selenide (ZnSe) is a promising material because of a high photoluminescence efficiency and wide spectral range emission in the visible region. In this work, ZnSe and Eu3+/Yb3+ co-doped ZnSe crystals were grown by the chemical vapour transport method. Photoluminescence and optical measurements revealed the effect of trivalent rare earth Eu3+/Yb3+ ions on the emission of new lines with enhancement intensity. In the photoluminescence spectrum, some sharp and intense lines were observed that allow for the possibility of covering a broad emission range. Moreover, the optical measurement showed a lower bandgap compared to that of pure ZnSe bulk crystal. This material is suitable for developing optoelectronic devices, which can emit light in the visible and near infrared range with an improved emission efficiency and wide tunability.

Laser Physics, 2019

This work focuses on assessing the analytical capabilities of a new photothermal lens method base... more This work focuses on assessing the analytical capabilities of a new photothermal lens method based on the self-mixing effect to reliably measure metallic traces in water-ethanol solutions. We compare it with the conventional thermal lens scheme, considering the low detection limit and versatility. A theoretical model is presented to describe the laser power variations as a function of the photothermal parameters of the analyzed sample. The experimental results demonstrate that the laser intensity variations, induced by the external optical feedback, are governed by the photothermal lens effect. Measurements of Fe(II)-1,10-phenanthroline in water–ethanol solutions show a favourable correspondence and agreement with the theory. The low detection limits obtained by the two analytic techniques also agree very well. Nevertheless, our instrument presents advantages regarding compactness and simplicity, suggesting that this platform could be potentially useful as a robust analytical tool for metallic trace detection. In addition, calibration of the method is performed by measuring the so-called self-mixing constant.

Journal of Environmental Management, 2019

In this work, we demonstrate for the first time that Thermal Lens Microscopy technique (TLM) can ... more In this work, we demonstrate for the first time that Thermal Lens Microscopy technique (TLM) can be applied to monitor the dynamics of a photocatalytic process in-situ. The photocatalytic reduction of hexavalent chromium-Cr(VI)-in aqueous solution using CdS and irradiated with visible light is monitored by TLM. Since the values of Cr(VI) concentration obtained after the photocatalytic process were close to those imposed by the international regulations for drinking water, the use of TLM allowed its measurement with a better reliability than with UV spectroscopy, usually used in this kind of analysis.

PLoS neglected tropical diseases, Dec 1, 2016

In this paper we report a quantitative laser Biospeckle method using VDRL plates to monitor the a... more In this paper we report a quantitative laser Biospeckle method using VDRL plates to monitor the activity of Trypanosoma cruzi and the calibration conditions including three image processing algorithms and three programs (ImageJ and two programs designed in this work). Benznidazole was used as a test drug. Variable volume (constant density) and variable density (constant volume) were used for the quantitative evaluation of parasite activity in calibrated wells of the VDRL plate. The desiccation process within the well was monitored as a function of volume and of the activity of the Biospeckle pattern of the parasites as well as the quantitative effect of the surface parasite quantity (proportion of the object's plane). A statistical analysis was performed with ANOVA, Tukey post hoc and Descriptive Statistics using R and R Commander. Conditions of volume (100μl) and parasite density (2-4x104 parasites/well, in exponential growth phase), assay time (up to 204min), frame number (11 ...

European Petroleum Conference, 1996

Physical Review B, 2013

We measure the current vs voltage (I-V) characteristics of a diodelike tunnel junction consisting... more We measure the current vs voltage (I-V) characteristics of a diodelike tunnel junction consisting of a sharp metallic tip placed at a variable distance d from a planar collector and emitting electrons via electric-field assisted emission. All curves collapse onto one single graph when I is plotted as a function of the single scaling variable V d −λ , d being varied from a few mm to a few nm, i.e., by about six orders of magnitude. We provide an argument that finds the exponent λ within the singular behavior inherent to the electrostatics of a sharp tip. A simulation of the tunneling barrier for a realistic tip reproduces both the scaling behavior and the small but significant deviations from scaling observed experimentally.

Polymers

A mode-mismatched thermal lens spectrometry (TLS) technique, in a pump–probe two-laser-beam confi... more A mode-mismatched thermal lens spectrometry (TLS) technique, in a pump–probe two-laser-beam configuration, was employed for the experimental determination of the thermal properties of four selected well-characterized polyolefin homopolymer films. We investigated the thermal diffusivity (D) and thermal conductivity (κ) of high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and polypropylene. We also measured the structural properties (i.e., average molecular weight, polydispersity index, branching number), along with the rheological and thermal properties (i.e., melting point, specific heat capacity Cp, degree of crystallinity) of samples by high-temperature gel permeation chromatography (HT-GPC), rheometric mechanical spectrometry (RMS), differential scanning calorimetry (DSC), and densitometry. The relationship between microstructural properties such as degree of crystallinity, D, and κ was investigated. The results show that there is good correlat...

Journal of Clinical & Experimental Dermatology Research, 2015

Nevus spilus or speckled lentiginous nevus is a mixed nevus and presents as a light-brown macule ... more Nevus spilus or speckled lentiginous nevus is a mixed nevus and presents as a light-brown macule with macular and/or papular-nodular lesions scattered across it. When lateralized, they can be associated with other anomalies, particularly neurological and musculoskeletal becoming the nevus spilus syndrome. We report a 16-year-old boy with a giant segmental nevus spilus associated with congenital spondylolysis.

Review of Scientific Instruments

We report a highly stable and affordable dual-wavelength digital holographic microscopy system ba... more We report a highly stable and affordable dual-wavelength digital holographic microscopy system based on common-path geometry. A Fresnel biprism is used to create an off-axis geometry, and two diode laser sources with different wavelengths λ1 = 532 nm and λ2 = 650 nm generate the dual-wavelength compound hologram. In order to extend the measurement range, the phase distribution is obtained using a synthetic wavelength Λ1 = 2930.5 nm. Furthermore, to improve the system's temporal stability and reduce speckle noise, a shorter wavelength (Λ2 = 292.5 nm) is used. The feasibility of the proposed configuration is validated by the experimental results obtained with Molybdenum trioxide, Paramecium, and red blood cell specimens.

Photonics

The emergence of diversified applications of laser-induced breakdown spectroscopy in the biomedic... more The emergence of diversified applications of laser-induced breakdown spectroscopy in the biomedical field, electronics, space physics, and material processing necessitates a comprehensive understanding of plasma parameters. The present work delineates the structure and evolution of copper plasma under different ambient pressures (0.01 mbar to 100 mbar) along with other plasma parameters. The study reveals the role of ambient pressure in the increase of plasma temperature (Te), electron density (Ne), number of particles in the Debye sphere, plasma frequency, inverse bremsstrahlung absorption coefficient, electron thermal velocity, electron–ion collision frequency and in the decrease of Debye length (λD) and plasma skin depth (PSD). The experimental techniques and the theoretical explanations for the variation of plasma parameters and their applications are also detailed. As the ambient pressure increases, the motion of plasma species becomes restricted, resulting in the increase of T...

Acquiring morphological and photothermal information is essential for characterization of a varie... more Acquiring morphological and photothermal information is essential for characterization of a variety of samples in biochemistry, material science and process technologies. In this paper, we report on the integration of digital holographic microscopy (DHM) and thermal lens (TL) spectrometry techniques enabling simultaneous measurement of both class of properties: morphological images and photothermal parameters. DHM in transmission mode is an effective technique for label-free, non-contact, real-time, and non-invasive imaging and measurement of phase objects, such as biomaterials. On the other hand, TL is a highly sensitive methodology to detect low concentrations of analytes in low absorbing samples. We demonstrate the usefulness of the DHM-TL integrated system by applying it to obtain morphometrical information of samples as well as for acquisition of their photothermal maps. Further, by extending the concept of “microsphere-assisted (MS) imaging” into TL, we show that MS-TL enables...

Photonics

Charge carriers’ generation from zinc includes silicon quantum dots (ZnSiQDs) layer sandwiched in... more Charge carriers’ generation from zinc includes silicon quantum dots (ZnSiQDs) layer sandwiched in-between porous silicon (PSi) and titania nanoparticles (TiO2NPs) layer-based solar cell is an efficient way to improve the cell’s performance. In this view, ZnSiQDs layer with various QDs sizes have been inserted, separating the PSi and TiO2NPs layers to achieve some graded bandgap quantum dot solar cells (GBQDSCs). In this process, ZnSiQDs of mean diameter 1.22 nm is first prepared via the top-down method. Next, ZnSiQDs have been re-grown using the bottom-up approach to get various mean diameters of 2.1, 2.7 and 7.4 nm. TiO2NPs of mean diameter in the range of 3.2 to 33.94 nm have been achieved via thermal annealing. The influence of different ZnSiQDs sizes on the designed GBGQDSCs performance has been determined. The proposed cell attains a short circuit current of 40 mA/cm2 and an efficiency of 4.9%. It has been shown that the cell performance enhances by optimizing the energy levels...

Optics and Lasers in Engineering

Journal of Cancer Science & Therapy, Mar 25, 2014

Review of Scientific Instruments, 2018

Journal of Physics D: Applied Physics, 2015

We report on the measurement of the thermal diffusivity, D, of few-layers graphene obtained by ch... more We report on the measurement of the thermal diffusivity, D, of few-layers graphene obtained by chemical vapor deposition, using a noncontact optical microscopy method based on a mode mismatched thermal lens technique in a pump-probe two-laser beams configuration. It takes advantage of the coaxial counter propagating tightly focused excitation and collimated probe beams in an improved thermal lens microscopy setup. The obtained results: D = (6.5 ± 0.09) × 10−4 m2 s−1, D = (1.9 ± 0.07) × 10−4 m2 s−1 and D = (1.3 ± 0.05) × 10−4 m2 s−1 for four (on a glass slide), eight and sixteen graphene (freestanding) layers are reasonable values, as can be concluded from reported literature data.

Nanomaterials

Herein, we report on a smart biosensing platform that exploits gold nanoparticles (AuNPs) functio... more Herein, we report on a smart biosensing platform that exploits gold nanoparticles (AuNPs) functionalized through ssDNA self-assembled monolayers (SAM) and the DNA-directed immobilization (DDI) of DNA-protein conjugates; a novel, high-sensitivity optical characterization technique based on a miniaturized gel electrophoresis chip integrated with online thermal lens spectrometry (MGEC-TLS), for the high-sensitivity detection of antigen binding events. Specifically, we characterized the physicochemical properties of 20 nm AuNPs covered with mixed SAMs of thiolated single-stranded DNA and bio-repellent molecules, referred to as top-terminated oligo-ethylene glycol (TOEG6), demonstrating high colloidal stability, optimal binder surface density, and proper hybridization capacity. Further, to explore the design in the frame of cancer-associated antigen detection, complementary ssDNA fragments conjugated with a nanobody, called C8, were loaded on the particles and employed to detect the pres...

Applied Sciences

Co-doped Zinc selenide (ZnSe) is a promising material because of a high photoluminescence efficie... more Co-doped Zinc selenide (ZnSe) is a promising material because of a high photoluminescence efficiency and wide spectral range emission in the visible region. In this work, ZnSe and Eu3+/Yb3+ co-doped ZnSe crystals were grown by the chemical vapour transport method. Photoluminescence and optical measurements revealed the effect of trivalent rare earth Eu3+/Yb3+ ions on the emission of new lines with enhancement intensity. In the photoluminescence spectrum, some sharp and intense lines were observed that allow for the possibility of covering a broad emission range. Moreover, the optical measurement showed a lower bandgap compared to that of pure ZnSe bulk crystal. This material is suitable for developing optoelectronic devices, which can emit light in the visible and near infrared range with an improved emission efficiency and wide tunability.

Laser Physics, 2019

This work focuses on assessing the analytical capabilities of a new photothermal lens method base... more This work focuses on assessing the analytical capabilities of a new photothermal lens method based on the self-mixing effect to reliably measure metallic traces in water-ethanol solutions. We compare it with the conventional thermal lens scheme, considering the low detection limit and versatility. A theoretical model is presented to describe the laser power variations as a function of the photothermal parameters of the analyzed sample. The experimental results demonstrate that the laser intensity variations, induced by the external optical feedback, are governed by the photothermal lens effect. Measurements of Fe(II)-1,10-phenanthroline in water–ethanol solutions show a favourable correspondence and agreement with the theory. The low detection limits obtained by the two analytic techniques also agree very well. Nevertheless, our instrument presents advantages regarding compactness and simplicity, suggesting that this platform could be potentially useful as a robust analytical tool for metallic trace detection. In addition, calibration of the method is performed by measuring the so-called self-mixing constant.

Journal of Environmental Management, 2019

In this work, we demonstrate for the first time that Thermal Lens Microscopy technique (TLM) can ... more In this work, we demonstrate for the first time that Thermal Lens Microscopy technique (TLM) can be applied to monitor the dynamics of a photocatalytic process in-situ. The photocatalytic reduction of hexavalent chromium-Cr(VI)-in aqueous solution using CdS and irradiated with visible light is monitored by TLM. Since the values of Cr(VI) concentration obtained after the photocatalytic process were close to those imposed by the international regulations for drinking water, the use of TLM allowed its measurement with a better reliability than with UV spectroscopy, usually used in this kind of analysis.

PLoS neglected tropical diseases, Dec 1, 2016

In this paper we report a quantitative laser Biospeckle method using VDRL plates to monitor the a... more In this paper we report a quantitative laser Biospeckle method using VDRL plates to monitor the activity of Trypanosoma cruzi and the calibration conditions including three image processing algorithms and three programs (ImageJ and two programs designed in this work). Benznidazole was used as a test drug. Variable volume (constant density) and variable density (constant volume) were used for the quantitative evaluation of parasite activity in calibrated wells of the VDRL plate. The desiccation process within the well was monitored as a function of volume and of the activity of the Biospeckle pattern of the parasites as well as the quantitative effect of the surface parasite quantity (proportion of the object's plane). A statistical analysis was performed with ANOVA, Tukey post hoc and Descriptive Statistics using R and R Commander. Conditions of volume (100μl) and parasite density (2-4x104 parasites/well, in exponential growth phase), assay time (up to 204min), frame number (11 ...

European Petroleum Conference, 1996

Physical Review B, 2013

We measure the current vs voltage (I-V) characteristics of a diodelike tunnel junction consisting... more We measure the current vs voltage (I-V) characteristics of a diodelike tunnel junction consisting of a sharp metallic tip placed at a variable distance d from a planar collector and emitting electrons via electric-field assisted emission. All curves collapse onto one single graph when I is plotted as a function of the single scaling variable V d −λ , d being varied from a few mm to a few nm, i.e., by about six orders of magnitude. We provide an argument that finds the exponent λ within the singular behavior inherent to the electrostatics of a sharp tip. A simulation of the tunneling barrier for a realistic tip reproduces both the scaling behavior and the small but significant deviations from scaling observed experimentally.

Polymers

A mode-mismatched thermal lens spectrometry (TLS) technique, in a pump–probe two-laser-beam confi... more A mode-mismatched thermal lens spectrometry (TLS) technique, in a pump–probe two-laser-beam configuration, was employed for the experimental determination of the thermal properties of four selected well-characterized polyolefin homopolymer films. We investigated the thermal diffusivity (D) and thermal conductivity (κ) of high-density polyethylene, low-density polyethylene, linear low-density polyethylene, and polypropylene. We also measured the structural properties (i.e., average molecular weight, polydispersity index, branching number), along with the rheological and thermal properties (i.e., melting point, specific heat capacity Cp, degree of crystallinity) of samples by high-temperature gel permeation chromatography (HT-GPC), rheometric mechanical spectrometry (RMS), differential scanning calorimetry (DSC), and densitometry. The relationship between microstructural properties such as degree of crystallinity, D, and κ was investigated. The results show that there is good correlat...