Markus Weiss - Academia.edu (original) (raw)

Papers by Markus Weiss

Nano letters, Jan 20, 2015

In graphene, the extremely fast charge carriers can be controlled by electron-optical elements, s... more In graphene, the extremely fast charge carriers can be controlled by electron-optical elements, such as waveguides, in which the transmissivity is tuned by the wavelength. In this work, charge carriers are guided in a suspended ballistic few-mode graphene channel, defined by electrostatic gating. By depleting the channel, a reduction of mode number and steps in the conductance are observed, until the channel is completely emptied. The measurements are supported by tight-binding transport calculations including the full electrostatics of the sample.

A beamline for circularly polarized radiation from a Sasaki type elliptical double undulator has ... more A beamline for circularly polarized radiation from a Sasaki type elliptical double undulator has been recently commissioned at BESSY-II. The PGM (Plane Grating Monochromator) based beamline works with collimated light and employs only one set of optical elements for steering and monochromatising the two (circularly) polarized, angularly separated, beams. The first commissioning results are presented here to illustrate the capabilities of this undulator-beamline concerning photon flux, photon energy resolution and polarization characteristics. .

Proceedings of the 1st International Conference on Energy-Efficient Computing and Networking - e-Energy '10, 2010

... We will discuss this issue and appropriate concepts and technologies in more detail in the fo... more ... We will discuss this issue and appropriate concepts and technologies in more detail in the following sections. 3. USING ICT TO INDUCE BEHAVIORAL CHANGE While automation and energy-optimized systems will doubtless be essential for achieving savings, the adoption of ...

Proceedings of the 8th International Conference on Mobile and Ubiquitous Multimedia - MUM '09, 2009

Reducing their energy consumption has become an important objective for many people. Consumption ... more Reducing their energy consumption has become an important objective for many people. Consumption transparency and timely feedback are essential to support those who want to adjust their behavior in order to conserve energy. In this work, we propose an interactive system that provides instantaneous feedback concerning the energy usage on household and device level. For that, we used and extended the capabilities of a smart electricity meter, built a web-based API to enable interoperability with other applications, and developed a mobile phone interface that allows users to monitor, control, and measure the consumption of single appliances. Our system illustrates a way how usage barriers can be lowered and how high user involvement can be created. By providing users the electricity feedback needed -in real-time and on device level -the system allows for identifying the biggest energy guzzlers and helps users decrease their energy consumption.

2012 12th IEEE International Conference on Nanotechnology (IEEE-NANO), 2012

ABSTRACT Liquid-gated graphene field-effect transistors (GFETs) with reliable performance are dev... more ABSTRACT Liquid-gated graphene field-effect transistors (GFETs) with reliable performance are developed. It is revealed that ideal defect-free graphene should be inert to electrolyte composition changes in solution, whereas a defective one responses to electrolyte composition. This finding sheds light on the large variety of pH or ion-induced gate shifts that have been published for GFETs in the recent literature. As a next step to target graphene-based (bio-) chemical sensing platform, non-covalent functionalization of graphene has to be introduced.

The Biochemical journal, Jan 15, 1998

Over the last few years, Pichia pastoris has been developed into a powerful expression system for... more Over the last few years, Pichia pastoris has been developed into a powerful expression system for a multitude of foreign genes. Here, we demonstrate that the P. pastoris expression system has similar power to the baculovirus expression system in high-level production of two G-protein-coupled receptors, the mouse 5HT5A 5-hydroxtryptamine receptor and the human beta2-adrenergic receptor. Different expression plasmids were constructed in which the cDNAs of the two receptors were cloned under the transcriptional control of the highly inducible promoter of the P. pastoris alcohol oxidase 1 (AOX1) gene. In three expression plasmids, the receptors were fused to the Saccharomyces cerevisiae alpha-factor prepropeptide and also to the c-myc tag or the FLAG tag to permit immunological detection of the receptors. After transformation into P. pastoris strains KM71 and SMD 1163, recombinant clones were selected and tested for the production of the 5HT5A receptor and the beta2-adrenergic receptor ...

Biological Chemistry Hoppe-Seyler, 1995

A thermostable aminoacylase (N-acylamino acid amidohydrolase, EC 3.5.1.14) from Bacillus stearoth... more A thermostable aminoacylase (N-acylamino acid amidohydrolase, EC 3.5.1.14) from Bacillus stearothermophilus was overexpressed in E. coli and characterized with respect to metal content, metal dependence, heat stability, and quaternary structure. Like other enzymes of the aminoacylase family, native aminoacylase contains one Zn2+ ion per subunit. Several other transition metal ions (Co2+, Mn2+ and Cd2+) also sustain aminoacylase activity toward N-acetyl L-alanine with Cd2+ giving the highest turnover number. The stability constants of the respective metal complexes were estimated by activity measurements in metal buffer systems. Co2+ also acts as an activator mainly by lowering the Km for the substrate. These data and CD spectra obtained with the native and the metal-free enzyme suggest a predominantly structural role for the intrinsic metal ion of thermostable aminoacylase. In contrast to previous reports the enzyme behaved as a dimer in analytical gel filtration.

Pichia Protocols, 1998

ABSTRACT Research in the field of membrane proteins has undergone explosive growth during the las... more ABSTRACT Research in the field of membrane proteins has undergone explosive growth during the last decade, primarily owing to the influence of the powerful techniques of modern molecular biology. Membrane proteins fulfill essential functions, such as communication, selective transport of metabolites and ions, and energy transformation. It is estimated that one-third of the genes of an organism encode integral membrane proteins (1). We are just now beginning to understand the molecular structures of this group of proteins and how they function within the confines of the cellular membranes. Among the different families of membrane proteins, the so-called G protein-coupled receptors (GPCRs) comprise the largest family. From the viewpoint of pharmacology, this family is of great importance, since about 60% of all pharmaceuticals known today mediate their effects via interaction with GPCRs. Therefore, much progress has been made in the characterization of the pharmacological and biochemical properties, as well as the signal transduction mechanisms of the GPCRs. Nevertheless, in order to understand the function and molecular dynamics of these receptors, detailed structural information will be needed. Despite the steady progress in understanding of GPCRs, solid three-dimensional (3D) structural data are still missing. To date, the crystallization and 3D determination have been successfully performed on only a handful of membrane proteins. All these structural determinations were performed on membrane proteins that are naturally highly expressed and can be purified in large quantities from their natural sources.

European journal of biochemistry / FEBS, 2002

The adenosine A(2a) receptor belongs to the seven transmembrane helix G-protein-coupled receptor ... more The adenosine A(2a) receptor belongs to the seven transmembrane helix G-protein-coupled receptor family, is abundant in striatum, vasculature and platelets and is involved in several physiological processes such as blood pressure regulation and protection of cells during anoxia. For structural and biophysical studies we have expressed the human adenosine A(2a) receptor (hA2aR) at high levels inserted into the Escherichia coli inner membrane, and established a purification scheme. Expression was in fusion with the periplasmic maltose-binding protein to levels of 10-20 nmol of receptor per L of culture, as detected with the specific antagonist ligand [(3)H]ZM241385. As the receptor C-terminus was proteolyzed upon solubilization, a protease-resistant but still functional receptor was created by truncation to Ala316. Addition of the sterol, cholesteryl hemisuccinate, allowed a stable preparation of functional hA2aR solubilized in dodecylmaltoside to be obtained, and, increased the stabi...

We investigate the magnetoresistance of epitaxially grown, heavily doped n-type GaAs layers with ... more We investigate the magnetoresistance of epitaxially grown, heavily doped n-type GaAs layers with thickness (40-50 nm) larger than the electronic mean free path (23 nm). The temperature dependence of the dissipative resistance Rxx in the quantum Hall effect regime can be well described by a hopping law (Rxx ∝ exp {−(T0/T ) p }) with p ≈ 0.6. We discuss this result in terms of variable range hopping in a Coulomb gap together with a dependence of the electron localization length on the energy in the gap. The value of the exponent p 0.5 shows that electron-electron interactions have to be taken into account in order to explain the occurrence of the quantum Hall effect in these samples, which have a three-dimensional single electron density of states.

ABSTRACT We have investigated the usability of a Coulomb blockade thermometer (CBT) at low temper... more ABSTRACT We have investigated the usability of a Coulomb blockade thermometer (CBT) at low temperatures around 50 mK and in high magnetic fields up to 27 Tesla. The experiments performed extend previous investigations both to lower temperatures and higher magnetic fields. We show that CBTs provide an easy way of magnetic field independent thermometry in an up to now problematic temperature range below the applicability of vapor pressure thermometry and above the working range of nuclear orientation thermometry, which are established methods of thermometry in magnetic fields.

Physical Review Letters, 2015

Artificial graphene consisting of honeycomb lattices other than the atomic layer of carbon has be... more Artificial graphene consisting of honeycomb lattices other than the atomic layer of carbon has been shown to exhibit electronic properties similar to real graphene. Here, we reverse the argument to show that transport properties of real graphene can be captured by simulations using "theoretical artificial graphene." To prove this, we first derive a simple condition, along with its restrictions, to achieve band structure invariance for a scalable graphene lattice. We then present transport measurements for an ultraclean suspended single-layer graphene pn junction device, where ballistic transport features from complex Fabry-Pérot interference (at zero magnetic field) to the quantum Hall effect (at unusually low field) are observed and are well reproduced by transport simulations based on properly scaled single-particle tight-binding models. Our findings indicate that transport simulations for graphene can be efficiently performed with a strongly reduced number of atomic sites, allowing for reliable predictions for electric properties of complex graphene devices. We demonstrate the capability of the model by applying it to predict so-far unexplored gate-defined conductance quantization in single-layer graphene.

British Journal of Pharmacology, 2015

Activation of the α7 nicotinic ACh receptor (nACh receptor) is considered an attractive target fo... more Activation of the α7 nicotinic ACh receptor (nACh receptor) is considered an attractive target for the treatment of cognitive impairment associated with neurological disorders. Here we describe the novel α7-nACh receptor agonist AQW051 as a promising drug candidate for this indication.

Physical Review B - PHYS REV B, 2002

The temperature driven flow lines of the diagonal and Hall magnetoconductance data (Gxx,Gxy) are ... more The temperature driven flow lines of the diagonal and Hall magnetoconductance data (Gxx,Gxy) are studied in heavily Si-doped, disordered GaAs layers with different thicknesses. The flow lines are quantitatively well described by a recent universal scaling theory developed for the case of particle-vortex duality symmetry. The separatrix Gxy=0.5 (in units e2/h) separates an insulating state from a quantum Hall-effect (QHE) state. The merging into the insulator or the QHE state at low temperatures happens along a semicircle separatrix G2xx+(Gxy-1/2)2=1/4, which is divided by an unstable fixed point at (Gxx,Gxy)=(1/2,1/2).

Solid State Communications, 2012

Semiconductor Science and Technology, 2006

We report the experimental realization of double quantum dots in singlewalled carbon nanotubes. T... more We report the experimental realization of double quantum dots in singlewalled carbon nanotubes. The device consists of a nanotube with source and drain contact, and three additional top-gate electrodes in between. We show that, by energizing these top-gates, it is possible to locally gate a nanotube, to create a barrier, or to tune the chemical potential of a part of the nanotube. At low temperatures we find (for three different devices) that in certain ranges of top-gate voltages our device acts as a double quantum dot, evidenced by the typical honeycomb charge stability pattern.

Nano letters, Jan 20, 2015

In graphene, the extremely fast charge carriers can be controlled by electron-optical elements, s... more In graphene, the extremely fast charge carriers can be controlled by electron-optical elements, such as waveguides, in which the transmissivity is tuned by the wavelength. In this work, charge carriers are guided in a suspended ballistic few-mode graphene channel, defined by electrostatic gating. By depleting the channel, a reduction of mode number and steps in the conductance are observed, until the channel is completely emptied. The measurements are supported by tight-binding transport calculations including the full electrostatics of the sample.

A beamline for circularly polarized radiation from a Sasaki type elliptical double undulator has ... more A beamline for circularly polarized radiation from a Sasaki type elliptical double undulator has been recently commissioned at BESSY-II. The PGM (Plane Grating Monochromator) based beamline works with collimated light and employs only one set of optical elements for steering and monochromatising the two (circularly) polarized, angularly separated, beams. The first commissioning results are presented here to illustrate the capabilities of this undulator-beamline concerning photon flux, photon energy resolution and polarization characteristics. .

Proceedings of the 1st International Conference on Energy-Efficient Computing and Networking - e-Energy '10, 2010

... We will discuss this issue and appropriate concepts and technologies in more detail in the fo... more ... We will discuss this issue and appropriate concepts and technologies in more detail in the following sections. 3. USING ICT TO INDUCE BEHAVIORAL CHANGE While automation and energy-optimized systems will doubtless be essential for achieving savings, the adoption of ...

Proceedings of the 8th International Conference on Mobile and Ubiquitous Multimedia - MUM '09, 2009

Reducing their energy consumption has become an important objective for many people. Consumption ... more Reducing their energy consumption has become an important objective for many people. Consumption transparency and timely feedback are essential to support those who want to adjust their behavior in order to conserve energy. In this work, we propose an interactive system that provides instantaneous feedback concerning the energy usage on household and device level. For that, we used and extended the capabilities of a smart electricity meter, built a web-based API to enable interoperability with other applications, and developed a mobile phone interface that allows users to monitor, control, and measure the consumption of single appliances. Our system illustrates a way how usage barriers can be lowered and how high user involvement can be created. By providing users the electricity feedback needed -in real-time and on device level -the system allows for identifying the biggest energy guzzlers and helps users decrease their energy consumption.

2012 12th IEEE International Conference on Nanotechnology (IEEE-NANO), 2012

ABSTRACT Liquid-gated graphene field-effect transistors (GFETs) with reliable performance are dev... more ABSTRACT Liquid-gated graphene field-effect transistors (GFETs) with reliable performance are developed. It is revealed that ideal defect-free graphene should be inert to electrolyte composition changes in solution, whereas a defective one responses to electrolyte composition. This finding sheds light on the large variety of pH or ion-induced gate shifts that have been published for GFETs in the recent literature. As a next step to target graphene-based (bio-) chemical sensing platform, non-covalent functionalization of graphene has to be introduced.

The Biochemical journal, Jan 15, 1998

Over the last few years, Pichia pastoris has been developed into a powerful expression system for... more Over the last few years, Pichia pastoris has been developed into a powerful expression system for a multitude of foreign genes. Here, we demonstrate that the P. pastoris expression system has similar power to the baculovirus expression system in high-level production of two G-protein-coupled receptors, the mouse 5HT5A 5-hydroxtryptamine receptor and the human beta2-adrenergic receptor. Different expression plasmids were constructed in which the cDNAs of the two receptors were cloned under the transcriptional control of the highly inducible promoter of the P. pastoris alcohol oxidase 1 (AOX1) gene. In three expression plasmids, the receptors were fused to the Saccharomyces cerevisiae alpha-factor prepropeptide and also to the c-myc tag or the FLAG tag to permit immunological detection of the receptors. After transformation into P. pastoris strains KM71 and SMD 1163, recombinant clones were selected and tested for the production of the 5HT5A receptor and the beta2-adrenergic receptor ...

Biological Chemistry Hoppe-Seyler, 1995

A thermostable aminoacylase (N-acylamino acid amidohydrolase, EC 3.5.1.14) from Bacillus stearoth... more A thermostable aminoacylase (N-acylamino acid amidohydrolase, EC 3.5.1.14) from Bacillus stearothermophilus was overexpressed in E. coli and characterized with respect to metal content, metal dependence, heat stability, and quaternary structure. Like other enzymes of the aminoacylase family, native aminoacylase contains one Zn2+ ion per subunit. Several other transition metal ions (Co2+, Mn2+ and Cd2+) also sustain aminoacylase activity toward N-acetyl L-alanine with Cd2+ giving the highest turnover number. The stability constants of the respective metal complexes were estimated by activity measurements in metal buffer systems. Co2+ also acts as an activator mainly by lowering the Km for the substrate. These data and CD spectra obtained with the native and the metal-free enzyme suggest a predominantly structural role for the intrinsic metal ion of thermostable aminoacylase. In contrast to previous reports the enzyme behaved as a dimer in analytical gel filtration.

Pichia Protocols, 1998

ABSTRACT Research in the field of membrane proteins has undergone explosive growth during the las... more ABSTRACT Research in the field of membrane proteins has undergone explosive growth during the last decade, primarily owing to the influence of the powerful techniques of modern molecular biology. Membrane proteins fulfill essential functions, such as communication, selective transport of metabolites and ions, and energy transformation. It is estimated that one-third of the genes of an organism encode integral membrane proteins (1). We are just now beginning to understand the molecular structures of this group of proteins and how they function within the confines of the cellular membranes. Among the different families of membrane proteins, the so-called G protein-coupled receptors (GPCRs) comprise the largest family. From the viewpoint of pharmacology, this family is of great importance, since about 60% of all pharmaceuticals known today mediate their effects via interaction with GPCRs. Therefore, much progress has been made in the characterization of the pharmacological and biochemical properties, as well as the signal transduction mechanisms of the GPCRs. Nevertheless, in order to understand the function and molecular dynamics of these receptors, detailed structural information will be needed. Despite the steady progress in understanding of GPCRs, solid three-dimensional (3D) structural data are still missing. To date, the crystallization and 3D determination have been successfully performed on only a handful of membrane proteins. All these structural determinations were performed on membrane proteins that are naturally highly expressed and can be purified in large quantities from their natural sources.

European journal of biochemistry / FEBS, 2002

The adenosine A(2a) receptor belongs to the seven transmembrane helix G-protein-coupled receptor ... more The adenosine A(2a) receptor belongs to the seven transmembrane helix G-protein-coupled receptor family, is abundant in striatum, vasculature and platelets and is involved in several physiological processes such as blood pressure regulation and protection of cells during anoxia. For structural and biophysical studies we have expressed the human adenosine A(2a) receptor (hA2aR) at high levels inserted into the Escherichia coli inner membrane, and established a purification scheme. Expression was in fusion with the periplasmic maltose-binding protein to levels of 10-20 nmol of receptor per L of culture, as detected with the specific antagonist ligand [(3)H]ZM241385. As the receptor C-terminus was proteolyzed upon solubilization, a protease-resistant but still functional receptor was created by truncation to Ala316. Addition of the sterol, cholesteryl hemisuccinate, allowed a stable preparation of functional hA2aR solubilized in dodecylmaltoside to be obtained, and, increased the stabi...

We investigate the magnetoresistance of epitaxially grown, heavily doped n-type GaAs layers with ... more We investigate the magnetoresistance of epitaxially grown, heavily doped n-type GaAs layers with thickness (40-50 nm) larger than the electronic mean free path (23 nm). The temperature dependence of the dissipative resistance Rxx in the quantum Hall effect regime can be well described by a hopping law (Rxx ∝ exp {−(T0/T ) p }) with p ≈ 0.6. We discuss this result in terms of variable range hopping in a Coulomb gap together with a dependence of the electron localization length on the energy in the gap. The value of the exponent p 0.5 shows that electron-electron interactions have to be taken into account in order to explain the occurrence of the quantum Hall effect in these samples, which have a three-dimensional single electron density of states.

ABSTRACT We have investigated the usability of a Coulomb blockade thermometer (CBT) at low temper... more ABSTRACT We have investigated the usability of a Coulomb blockade thermometer (CBT) at low temperatures around 50 mK and in high magnetic fields up to 27 Tesla. The experiments performed extend previous investigations both to lower temperatures and higher magnetic fields. We show that CBTs provide an easy way of magnetic field independent thermometry in an up to now problematic temperature range below the applicability of vapor pressure thermometry and above the working range of nuclear orientation thermometry, which are established methods of thermometry in magnetic fields.

Physical Review Letters, 2015

Artificial graphene consisting of honeycomb lattices other than the atomic layer of carbon has be... more Artificial graphene consisting of honeycomb lattices other than the atomic layer of carbon has been shown to exhibit electronic properties similar to real graphene. Here, we reverse the argument to show that transport properties of real graphene can be captured by simulations using "theoretical artificial graphene." To prove this, we first derive a simple condition, along with its restrictions, to achieve band structure invariance for a scalable graphene lattice. We then present transport measurements for an ultraclean suspended single-layer graphene pn junction device, where ballistic transport features from complex Fabry-Pérot interference (at zero magnetic field) to the quantum Hall effect (at unusually low field) are observed and are well reproduced by transport simulations based on properly scaled single-particle tight-binding models. Our findings indicate that transport simulations for graphene can be efficiently performed with a strongly reduced number of atomic sites, allowing for reliable predictions for electric properties of complex graphene devices. We demonstrate the capability of the model by applying it to predict so-far unexplored gate-defined conductance quantization in single-layer graphene.

British Journal of Pharmacology, 2015

Activation of the α7 nicotinic ACh receptor (nACh receptor) is considered an attractive target fo... more Activation of the α7 nicotinic ACh receptor (nACh receptor) is considered an attractive target for the treatment of cognitive impairment associated with neurological disorders. Here we describe the novel α7-nACh receptor agonist AQW051 as a promising drug candidate for this indication.

Physical Review B - PHYS REV B, 2002

The temperature driven flow lines of the diagonal and Hall magnetoconductance data (Gxx,Gxy) are ... more The temperature driven flow lines of the diagonal and Hall magnetoconductance data (Gxx,Gxy) are studied in heavily Si-doped, disordered GaAs layers with different thicknesses. The flow lines are quantitatively well described by a recent universal scaling theory developed for the case of particle-vortex duality symmetry. The separatrix Gxy=0.5 (in units e2/h) separates an insulating state from a quantum Hall-effect (QHE) state. The merging into the insulator or the QHE state at low temperatures happens along a semicircle separatrix G2xx+(Gxy-1/2)2=1/4, which is divided by an unstable fixed point at (Gxx,Gxy)=(1/2,1/2).

Solid State Communications, 2012

Semiconductor Science and Technology, 2006

We report the experimental realization of double quantum dots in singlewalled carbon nanotubes. T... more We report the experimental realization of double quantum dots in singlewalled carbon nanotubes. The device consists of a nanotube with source and drain contact, and three additional top-gate electrodes in between. We show that, by energizing these top-gates, it is possible to locally gate a nanotube, to create a barrier, or to tune the chemical potential of a part of the nanotube. At low temperatures we find (for three different devices) that in certain ranges of top-gate voltages our device acts as a double quantum dot, evidenced by the typical honeycomb charge stability pattern.