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In this work we present results concerning the fundamental equations of charge-carrier transport in semiconductor structures. We discuss a correct modeling of the recombination terms that does not violate the charge conservation law. We obtained that under stationary conditions and equal generation rates of electrons and holes the recombination rates of both kinds of carriers must be matched. Under low excitation conditions (linear regime) the recombination rate can be expressed as a linear combination of the excess concentrations of electrons and holes, and only in very precise situations can a lifetime be defined. Explicit calculation of the charge variation was carried out within the framework of the band-to-band and Shockley-Read-Hall statistics. It is shown that the bulk space charge established on distances of the order of Debye’s length cannot influence the current-voltage characteristics of a device in a linear regime. It was also shown that metal-p-type semiconductor contacts are essentially different from those made on n-type semiconductors. The former should be considered as having a bipolar semiconductor structure and recombination cannot be neglected. The boundary conditions for the Poisson equation are presented. [ABSTRACT FROM AUTHOR]

Models used for describing generation and recombination of electrons and holes do not agree with the Maxwell's electrodynamics. Some modifications are required for depicting the generation and recombination phenomenon, in order to be consistent with the Maxwell's equations and there is a need for replacing standard expressions for recombination involving lifetimes and holes.

The functioning of the solar cells (and photoelectric phenomena in general) relies on the photo-generation of carriers in p-n junctions and their subsequent recombination in the quasi-neutral regions. A number of basic issues concerning the physics of the operation of solar cells still remain obscure. This paper reports on some unsolved basic problems, namely: a model of the recombination processes that does not contradict Maxwell's equations; boundary conditions; the role played by space charges in the transport phenomena, and the formation of quasi-neutral regions under the presence of nonequilibrium photo-generated carriers. In this work, a new formulation of the theory that explains the underlying physical phenomena involved in the generation of a photo-e.m.f. is presented. [ABSTRACT FROM AUTHOR]

A general approach to study of energy interaction between hot electrons and phonons is presented. Basing on kinetic equations for both subsystems of these quasiparticles we suggest the most convenient models for the theoretical investigation of hot electrons as well as of hot phonons. All of these models are based on possibility of obtaining the symmetric part of nonequilibrium distribution function in the form of the Dirac function (for electrons) or the Planck function (for phonons) with own nonequilibrium local temperatures. General equations are obtained for these temperatures. [ABSTRACT FROM AUTHOR]

Background. Meningiomas may be accompanied by peritumoral edema. Incidence and pathogenesis of edema are nor clearly established. Prevalence and severity of edema vary significantly in patients with meningiomas similar in various parameters., Objective: To assess peritumoral edema in intracranial meningiomas and factors influencing incidence and severity of this process., Material and Methods: There were 126 patients (69% women) aged 19-76 years (median 53), who were diagnosed with 142 meningiomas. Patients underwent surgery ( n =111) and radiotherapy ( n =15) in 2016-2018. The MRI protocol included T1, T2, T2-FLAIR, DWI and post-contrast T1-weighted images in three projections, diffusion tensor MRI in 27 cases and MR spectroscopy in 21 patients., Results: Peritumoral edema was detected in 46% ( n =66) of cases including 21 (31%) patients with severe edema. The ALPS index was 1.510±0.1931 in meningiomas without edema and 1.308±0.19 in those with edema ( p =0.014). There was positive correlation between edema, dimensions and uneven contours of meningioma, as well as negative correlation with CSF cleft sign. Blood flow velocity was higher in atypical and anaplastic meningiomas with edema ( p =0.03). Other signs (localization, histological variant, malignancy grade, characteristics of MR signal, peaks of the main metabolites, diffusion and perfusion parameters of tumor) did not significantly affect peritumoral edema in patients with meningiomas ( p >0.05)., Conclusion: Diffusion tensor tomography with ALPS index revealed significant effect of glymphatic system dysfunction on peritumoral edema. Large meningioma with uneven contours increased the risk of peritumoral edema, while CSF cleft sign reduced this risk. Other factors did not affect cerebral edema in meningiomas.

Intraoperative recording of cortico-cortical evoked potentials (CCEPs) enables studying effective connections between various functional areas of the cerebral cortex. The fundamental possibility of postoperative speech dysfunction prediction in neurosurgery based on CCEP signal variations could serve as a basis to develop the criteria for the physiological permissibility of intracerebral tumors removal for maximum preservation of the patients' quality of life. The aim of the study was to test the possibility of predicting postoperative speech disorders in patients with glial brain tumors by using the CCEP data recorded intraoperatively before the stage of tumor resection., Materials and Methods: CCEP data were reported for 26 patients. To predict the deterioration of speech functions in the postoperative period, we used four options for presenting CCEP data and several machine learning models: a random forest of decision trees, logistic regression, and support vector machine method with different types of kernels: linear, radial, and polynomial. Twenty variants of models were trained: each in 300 experiments with resampling. A total of 6000 tests were performed in the study., Results: The prediction quality metrics for each model trained in 300 tests with resampling were averaged to eliminate the influence of "successful" and "unsuccessful" data grouping. The best result with F1-score = 0.638 was obtained by the support vector machine with a polynomial kernel. In most tests, a high sensitivity score was observed, and in the best model, it reached a value of 0.993; the specificity of the best model was 0.370., Conclusion: This pilot study demonstrated the possibility of predicting speech dysfunctions based on CCEP data taken before the main stage of glial tumors resection; the data were processed using traditional machine learning methods. The best model with high sensitivity turned out to be insufficiently specific. Further studies will be aimed at assessing the changes in CCEP during the operation and their relationship with the development of postoperative speech deficit., Competing Interests: Conflicts of interest. The authors declare no conflicts of interest.

Objective: Mapping of effective speech connections between the frontal and temporal lobes with cortico-cortical evoked potentials., Material and Methods: There were 3 patients with brain tumors in the left frontoparietal region. The neoplasms were localized in the dominant hemisphere near cortical speech centers and pathways. Cortico-cortical evoked potentials were intraoperatively recorded in response to bipolar stimulation with a direct current delivered through the subdural electrodes (single rectangular biphasic impulses with duration of 300 μs and frequency of 1 Hz). Stimulation intensity was gradually increased from 2 mA within 3-4 mA. Registration was carried out by averaging ECoG (30-50 stimuli in each session) in the 300-ms epoch after stimulus. Direct cortical stimulation was used to validate the results of cortico-cortical speech mapping with cortico-cortical evoked potentials., Results: In our cases, we obtained cortico-cortical evoked potentials from inferior frontal gyrus after stimulation of superior temporal gyrus. In one case, this effective relationship was unidirectional, in the other two patients reciprocal. Mean latency of N1 peak was 65 ms (range 49.6-90 ms), mean amplitude 71 µV (range 50-100 µV). Cortico-cortical mapping data were confirmed by detection of Broca's area in 2 out of 3 cases out during direct cortical stimulation with maximum amplitude of N1 wave. «Awake craniotomy» protocol was applied. In one case, Broca's area was not detected during direct stimulation. No postoperative speech impairment was noted., Conclusion: Initial results of cortical mapping with cortico-cortical evoked potentials in a small sample confirmed its practical significance for analysis of cortical projections of effective speech communications between the frontal and temporal lobes. Further study of this method in large samples is required.