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In this paper, the photoconductive parameters of Field-Effect Transistors (FETs) excited by high-frequency optical source is studied. The FETs plasma oscillations dominated in the Terahertz (THz) range demonstrates their important effect related to THz emission and detection at room temperature. The study taking into account the plasma modes of FETs which can be coupled with photoexcitation optical pulse. Particularly, the model using the excess carriers flow through the traps density and the small-signal response of Field-Effect Transistors to describe the photoconductivity and the drain current in external circuit. The effect of the carriers relaxation time, the excited wavelength and the channel plasma modes on photoexcited FETs behavior is investigated. This leads to the possibilities of increasing the photoconductive contribution in total current by coupling both the microwave and optical FET proprieties.

A study of the small-signal response of a Field-Effect Transistor connected to a purely reactive load is proposed. In particular, this model, using the equivalent admittances approach, is applied to a transistor connected to an inductance L, a capacitance C and LC resonant and anti-resonant circuits. The influence of such frequency-dependent load on the dynamics of the transistor, dominated in the terahertz range by collective plasma behavior, is investigated. This leads to the possibilities of shifting, amplifying or softening resonances appearing in the voltage gain spectrum. The effect of a resistive part of the load is also estimated.

Chimeric antigen receptor (CAR)-redirected T lymphocytes are a promising immunotherapeutic approach and object of pre-clinical evaluation for the treatment of acute myeloid leukemia (AML). We developed a CAR against CD123, overexpressed on AML blasts and leukemic stem cells. However, potential recognition of low CD123-positive healthy tissues, through the on-target, off-tumor effect, limits safe clinical employment of CAR-redirected T cells. Therefore, we evaluated the effect of context-dependent variables capable of modulating CAR T cell functional profiles, such as CAR binding affinity, CAR expression, and target antigen density. Computational structural biology tools allowed for the design of rational mutations in the anti-CD123 CAR antigen binding domain that altered CAR expression and CAR binding affinity without affecting the overall CAR design. We defined both lytic and activation antigen thresholds, with early cytotoxic activity unaffected by either CAR expression or CAR affinity tuning but later effector functions impaired by low CAR expression. Moreover, the anti-CD123 CAR safety profile was confirmed by lowering CAR binding affinity, corroborating CD123 is a good therapeutic target antigen. Overall, full dissection of these variables offers suitable anti-CD123 CAR design optimization for the treatment of AML.

We investigate the shortening of the gate-length in submicrometric and nanometric field-effect transistors as a powerful tool to improve their self-oscillations performances in the terahertz frequency region due to the appearance of the Dyakonov–Shur instability. The theoretical model is based on the numerical solution of hydrodynamic equations for the electron transport in FETs/HEMTs channels. We show that a decrease of the gate length allows, on the one hand, to increase the intrinsic resonant frequencies near 1 THz and, on the other hand, to improve the conditions for the onset of the Dyakonov–Shur instability and related phenomena. The small-signal characteristics calculated under constant drain-voltage operation are compared with the drain-voltage self-oscillations calculated under constant drain-current operation.

The ribonucleoprotein (RNP) domain is one of the most common eukaryotic protein domains, and is found in many proteins involved in recognition of a wide variety of RNAs. Two structures of RNA complexes of human U1A protein have revealed important aspects of RNP-RNA recognition, but have also raised intriguing questions concerning how RNP domains discriminate between different RNAs. In this work, we extend the investigation of U1A-RNA recognition by comparing the dynamics of U1A protein both free and in complex with RNA. We have also investigated the trimolecular complex between two U1A proteins and the complete polyadenylation inhibition element to study the effect of RNA-dependent protein-protein interactions on protein conformational flexibility. We report that changes in backbone dynamics upon complex formation identify regions of the protein where conformational exchange processes are quenched in the RNA-bound conformation. Furthermore, amino acids whose side-chains experience significant changes in conformational flexibility coincide with residues particularly important for the specificity of the U1A protein/RNA interaction. This study adds a new dimension to the description of the coordinated changes in structure and dynamics that are critical to define the biological specificity of U1A and other RNP proteins.

We review recent results concerning the microscopic analysis of electronic noise in semiconductor unipolar structures in the frequency range where 1/f noise can be neglected. Calculations are based on a Monte Carlo simulator of the carrier motion self-consistently coupled with a Poisson solver. Both current- and voltage-noise operation modes are considered and their respective advantages illustrated. The analysis is applied to structures with increasing degree of complexity, that is: homogeneous materials, resistors, n+ nn+ diodes., Schottky-barrier diodes and GaAs MESFETs. The main sources of noise like diffusion, generation-recombination, coupling between velocity and local electric field fluctuations, etc. are treated in the presence of electric fields of arbitrary strength. Results should constitute the basis for a physical interpretation of electronic noise in most semiconductor materials and devices thus providing inputs for improving quality and reliability figures of merit.

We present a detailed analysis of current and number fluctuations in submicron n + nn + Si structures at different bias voltages and lengths of the active region. The calculation is carried out by coupling self-consistently a one-dimensional Poisson solver with a three-dimensional Ensemble Monte Carlo simulator. The coupling between fluctuations in carrier velocity and in the self-consistent field is found to be responsible for a negative part (a minimum) in the autocorrelation function of current fluctuations at equilibrium. The fluctuations of the carrier number in different slices and in the whole structure are influenced by space-charge effects and by the inhomogeneity of the structure. They are found to be a sensitive probe for characterizing different contact models. With increasing applied voltage the coupling between velocity and electric-field fluctuations weakens due to a less effective screening.

We present a theoretical calculation of the current correlation functions and the associated noise spectra of a quasi one-dimensional system terminated by ideal contacts. The shape of the correlation functions is directly related to the microscopic carrier dynamics. When applying a voltage we find: In the classical limit the low-frequency noise spectrum recovers the well-known shot noise formula at high voltages. In the degenerate limit it is suppressed due to quantum-mechanical correlations. The extension of the theory to a multi-subband system shows that in the presence of an applied voltage the step height of the low-frequency spectral density is reduced to one half of its equilibrium value.

We present a general theory to investigate the electronic noise in the presence of scattering as well of generation recombination processes under the application of an electric field of arbitrary strength. An exact decomposition procedure of the current spectral density is given which, in addition to fluctuations in carrier velocity and number, shows the presence of a cross term coupling both fluctuations. Four correlation functions are thus found to be needed to evaluate all terms. To this purpose, the Monte Carlo method is shown to provide a unifying microscopic calculation of these functions and thus of each term contributing to the total spectral density. In this way, scatterings in the conducting band as well as capture to and release from the traps are treated for the first time on the same kinetic level of description. In particular, the Poole-Frenkel effect is included when necessary. As an application, we consider the case of p-Si at77 K with a generation-recombination mechanism given by the capture at shallow impurities assisted by acoustic phonons. Then, the theoretical results are compared with existing mesoscopic theories as well as with available experimental results.

We present a theoretical analysis of the thermal conductivity of charge carriers in semiconductors under nonequilibrium conditions due to an applied electric field. The theory is based on a correlation-function formalism which directly relates this kinetic coefficient to four spectral densities involving carrier velocity and energy flux fluctuations. Monte Carlo calculations performed for the cases of p-Si and n-GaAs give an evidence of a strong dependence of the thermal conductivity on increasing electric fields.

We present a Monte Carlo procedure which, by including the mechanism of generation and recombination from impurity centers, enables us to calculate directly from the simulation the field dependent conductivity for the first time. The reliability of the theoretical model has been checked by comparing numerical results with experiments provided by the Montpellier group and performed on p-Si at different acceptor concentrations and temperatures.