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The tight-binding approximation is employed here to investigate electronic bulk and edge ('surface') states in semi-infinite graphene sheets and graphene monolayer ribbons with various edge terminations (zigzag, horseshoe, and armchair edges). It is shown that edge states do not exist for a uniform hopping (transfer) matrix. The problem is generalized to include edge elements of the hopping matrix distinct from the infinite-sheet ('bulk') ones. In this case, semi-infinite graphene sheets with zigzag or horseshoe edges exhibit edge states, while semi-infinite graphene sheets with armchair edges do not. The energy of the edge states lies above the (zero) Fermi level. Similarly, symmetric graphene ribbons with zigzag or horseshoe edges exhibit edge states, while ribbons with asymmetric edges (zigzag and horseshoe) do not. It is also shown how to construct the 'reflected' solutions (bulk states) for the intervening equations with finite differences both for semi-infinite sheets and ribbons. PACS Nos.: 73.22.Pr, 73.20.At, 61.48.Gh, 72.80.Vp. Nous utilisons l'approximation des liaisons fortes pour etudier les etats electroniques dans la masse et en surface (bordure) dans des feuilles semi-infinies de graphene et des rubans monocouches avec differentes terminaisons, de type zig-zag, fer a cheval ou chaise. Nous montrons que les etats de surface n'existent pas pour une matrice de transfert (hopping) uniforme. Le probleme est ici generalise pour inclure des elements de bordure de la matrice de transfert distincts de ceux de la feuille infinie (de masse). Dans ce cas, les feuilles semi-infinies avec bordures en zig-zag ou en fer a cheval ont des etats de surface, ce que n'ont pas ceux avec bordure de type chaise. L'energie des etats de bordure-surface est au dessus du niveau (zero) de Fermi. De meme, les rubans de graphene symetriques avec bordure de type zig-zag ou fer fi cheval ont des etats de surface, alors que ceux avec bordures asymetriques (zig-zag ou fer a cheval) n'en ont pas. Nous montrons egalement comment construire les solutions reflechies (dans la masse) pour les equations intervenantes aux differences finies, a la fois pour les feuilles semi-infinies et les rubans. [Traduit par le Redaction], 1. Introduction Because graphene occurs as small pieces, finite-size effects in graphene are relevant. We consider here graphene single-sheet ribbons with various edge terminations (zig-zag, horseshoe, or armchair edges). For [...]

The screening, the configurational correlations and the interaction correlations in the theory of binary electrolytes are examined, by exploiting the charge conservation and the properties of the equilibrium state. Validity conditions for the linearised Debye–Huckel screened potential are provided. A non-zero ionic radius is employed in order to account for solvation effects, and limitations on the contribution of the ionic radius are derived. A possible stabilisation of the ions in equilibrium positions, arising from counterion configurational correlations, is analysed for associated electrolytes, and the corresponding correlation energy is derived. A van der Waals-type equation is presented for strong electrolytes. Some well-known technical difficulties of the theory of electrolytes are revisited, with emphasis on statistical-dynamical correlations, excluded volume and multiple-boundary conditions. [ABSTRACT FROM AUTHOR]

Hemangioblastoma is a rare, benign, highly vascularized tumour, that usually presents a muriform nodule. The most frequent localization is the posterior cranial fossa. The frequency of this spinal lesion is very low, representing less than 5% of spinal cord tumours. The presentation of hemangioblastoma can widely vary, from a solid tumour to a lesion with a cystic component. We present the case of a 43 years old patient, admitted to our clinic for left hemiparesis, swallowing disorders, and dysphonia. An MRI is performed and it showed a cervicomedullary junction tumour with a solid nodule and an anterior cystic cavity pushing towards the 4th ventricle. The patient underwent surgery for the total removal of the tumour. Post-operative CT confirmed the total ablation of the tumour. The patient is discharged with improved symptomatology. In the last 10 years, in our clinic were admitted 23 cases of hemangioblastoma, 14 males (61% of the patients) and 9 females (39%) with an age at presentation varied from 14 to 78 years (mean 48,2 years). Only 3 patients (13%) out of the 23 had associated von Hippel-Lindau syndrome, with hemangioblastomas also present in other locations. The most common location was the posterior fossa, in 13 cases (56,6%). Headache (69,5%), ataxia (56%) and balance disorders (52%) were the most common symptoms accused by patients. The followup varied from 6 to 84 months (mean 20 months). Only one patient died during hospitalization and one tumour recurrence was noted. Most patients improved or remained clinically stable postoperatively. [ABSTRACT FROM AUTHOR]

Glomus jugulare tumours are extremely rare, slow-growing, hypervascular tumours that arise within the jugular foramen of the temporal bone and frequently involve the lower cranial nerves. We performed a retrospective study for patients treated between January 2005 and December 2019, reviewing clinical and radiological data for 91 cases of glomus jugulare tumours. Data were available for 91 patients presenting with 96 tumours. Surgery was 1st intention of treatment for 13 cases, the endovascular approach was 1st intention for 6 cases and GKRS was primarily performed in 72 cases. Combined treatment options were used in 19 cases. The median age at the time of treatment was of 57 years. The tumour volume varied between 0.5 and 73.4 cm3 with a median value of 8.3 cm3. For the cases treated with GKRS, the peripheral dose ranged between 8 and 35 Gy on the 35% to 65% isodose, with a median of 14 Gy on the 45% isodose. The average follow-up was 38 months with a maximum of 94 and consisted of contrast-enhanced MRI every six months in the first year after the procedure and every 1 to 2 years afterwards. The overall tumour control rate was 95.6% using multimodal treatment options for glomus jugulare tumours. Multimodal treatment for glomus jugulare tumours offers the patient the chance for the best possible outcome and long-term survivability. An individual treatment approach for this kind of very rare head and neck tumour (0,6% of all head and neck tumours) is recommended to choose the best risk-versus-benefit treatment option. [ABSTRACT FROM AUTHOR]

Background: Diffuse gliomas are the most frequent primary central nervous system (CNS) neoplasms, originating from the parenchyma itself, oligodendrogliomas accounting for approximately 10% of cerebral gliomas. For the past 20 years, the study of genetic/molecular mechanisms of glioma genesis and progression has gradually come into focus. However, the biological and clinical significance of these mutations are still to be completely characterized. The purpose of this article is to describe our clinical experience with oligodendrogliomas and to review the current literature, in order to better describe the characteristics of the molecular/genetic oligodendroglioma subgroups. Methods: We performed a single-institution retrospective study that included 66 patients with oligodendrogliomas operated in our department between January 2011 and December 2018. Results: Our study included 26 female patients (39%) and 40 male patients (59%). The mean age at presentation was 39.9year-old (range 26-59year-old). The tumours were located predominantly in the right hemisphere (53%), the majority being situated in the frontal lobe (59%). 64% of the patients had signs of mass effect on the imaging studies, 13% presented with brain herniation syndromes, and 16 % of the surgically treated patients had a relapse with regrowth and malignant transformation of the tumour. The most common complaint that the patients had at admission was a headache. Seizures were the second most common symptom that determined the patients to seek medical attention. Conclusion: The expanding knowledge regarding the genetic alterations of oligodendroglial tumours could lead to significant changes in treatment strategies. However, the utility of each particular marker in planning the treatment has yet to be established. Emerging data will, most likely, improve outcome prediction and adjuvant therapy strategies by identifying the patients most likely to benefit from a particular treatment. [ABSTRACT FROM AUTHOR]

Meningiomas are tumors of the meninges that arise primarily from arachnoidal cap cells, but they can also occur rarely as primary tumors in other localizations, such as within the ventricles. They stand for 24-30% of primary intracranial tumors and affect mostly women in their middle age or later adult life [1, 2]. Meningiomas can be classified, according to World Health Organization (WHO) classification of Central Nervous System (CNS) tumors, as benign (grade I, most frequently encountered type), atypical (grade II) or anaplastic (grade III), based mostly on histopathological criteria known to be associated with tumor progression, recurrence risk and survival. Since meningioma grading based on the WHO classification is the most important factor determining therapeutic management and tumor prognosis, there has been an increasing interest in adding new criteria for better characterization of these tumors. Thus, the 2016 edition of WHO classification recognized brain invasion as an independent criterion for atypical (grade II) meningioma diagnosis [3]. However, meningiomas that display aggressive features such as rapid growth and higher recurrence rate, can also involve blood vessels and bone. Hence, the authors aim to describe a different entity, aggressive meningiomas, not previously listed as a tumor phenotype in the WHO classification of meningothelial-cell tumors, with regard to pre-, intraand postoperative methods for diagnosis and explore the implications on surgical strategies and adjuvant therapy. MATERIALS AND METHODS We performed a single-center retrospective study. We reviewed the files of all patients diagnosed with primary intracranial meningioma at the 4th Clinical Department of Neurosurgery, Bagdasar-Arseni Clinical Emergency Hospital, between January 2013 and December 2018 and identified the cases of aggressive meningiomas, characterized by either: invasion into the brain parenchyma, involvement of the major blood vessels, cranial vault bone lysis without involvement of the outer table of the skull or complete bone destruction and aesthetic deformity, as showed by preoperative imaging and confirmed by histopathological examination. RESULTS We identified 291 patients with tumors meeting the required imagistic/histopathological criteria, from which we selected 2 representative cases for the current articles, aiming to better describe this tumor entity regarding pre-, intra- and postoperative aspect and therapeutic strategy. [ABSTRACT FROM AUTHOR]

Meningiomas are common neoplasms of the central nervous system, comprising between 24 and 30% of primary intracranial tumors, most commonly affecting females in their middle age or later adult life [1] [2]. Meningiomas are classified as benign, atypical or anaplastic meningiomas depending mostly on histopathological criteria known to be associated with worse prognosis in terms of tumor progression, recurrence risk after surgery and overall survival. The 2016 edition of World Health Organization (WHO) classification of Central Nervous System (CNS) tumors recognizes brain invasion as an independent criterion for diagnosing an atypical grade II meningioma [3]. Meningioma grading based on the WHO classification of CNS tumors thoroughly impacts therapeutic management and tumor prognosis. Aggressive meningiomas, a different phenotype of tumors, characterized by rapid growth and involvement of adjacent brain tissue, blood vessels and bone, was not previously listed as an independent entity in the WHO classification of meningothelial-cell tumors. Regarding the increasing importance of tumor grading in meningioma treatment strategies, the authors here provide an overview of clinicopathological and radiographic features, surgical management and long-term prognosis of this novel meningothelial tumor entity, the aggressive meningioma. In particular, we aimed to describe pre-, intra- and postoperative methods for recognizing aggressive meningiomas and explore the implications of this diagnosis on both surgical strategies and adjuvant therapy. [ABSTRACT FROM AUTHOR]

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The formation of polariton wave-packets created by high-intensity laser beams focused in plasmas is analyzed, and the velocity, energy, size, structure, stability, and electron content of such polaritonic pulses are characterized. It is shown that polaritonic pulses may transport trapped electrons with appreciable energies, provided the medium behaves as a rarefied classical plasma. The relativistic electron energy is related to the polariton group velocity, which is close to the velocity of light in this case. The plasma pulse is polarized, and the electron number in the pulse is estimated as being proportional to the square root of the laser intensity and the 3/2-power of the pulse size. It is shown that Compton (Thomson) backscattering by such polaritonic pulses of electrons may produce coherent X- and gamma rays, as a consequence of the quasirigidity of the electrons inside the polaritonic pulses and their relatively large number. The classical results of the Compton scattering are re-examined in this context, the energy of the scattered photons and their cross-section are analyzed, especially for backscattering, the great enhancement of the scattered flux of X- or gamma rays due to the coherence effect is highlighted and numerical estimates are given for some typical situations. [ABSTRACT FROM AUTHOR]

A special mechanism of thermoelectric transport is described, consisting of pulses of charge carriers which “fly” periodically through the external circuit from the hot end of the sample to the cold end, with a determined duration of the “on” and “off” times of the electric contacts, while maintaining continuously the thermal contacts. It is shown that such a “resonant” ideal thermogenerator may work cyclically, with the same efficiency quotient as the ideal efficiency quotient of the thermoelectric devices operated in the usual stationary transport regime but the electric flow and power are increased, as a consequence of the concentration of the charge carriers on pulses of small spatial extent. The process is reversible, in the sense that it can be operated either as a thermoelectric generator or as an electrothermal cooler. [ABSTRACT FROM AUTHOR]

The fundamental equations of thermoelectricity and the efficiency quotient of the thermoelements emphasizing the relevance of the figure of merit parameter are reported. The results revealed that the efficiency quotient is always lower than the Carnot efficiency quotient and the new figure of merit has never exceeded unity.

• Ion-ion interaction potentials are derived for a classical plasma. • Total energy of a classical plasma is computed. • Solid phase occurs for a classical plasma. • The precursory liquid phase is identified and a van der Waals equation is established for a classical plasma. A linearized self-consistent variational approach is employed to investigate the (thermodynamic) stability of a classical plasma (electrons and positive ions). It is shown, by using this approach, that a classical plasma, which consists of ions "dressed" with electrons, has a well-defined thermodynamics. In the strong-coupling regime the "plasma" is a solid, while, on passing to the weak-coupling regime, it becomes gradually a liquid, a non-ideal gas, and, finally, in the weak-coupling limit, it behaves as an ideal classical gas. A van der Waals-type equation is established for the plasma non-ideal gas. [ABSTRACT FROM AUTHOR]

The Goeppert-Mayer and Kramers-Henneberger transformations are examined for bound charges placed in electromagnetic radiation in the nonrelativistic approximation. The consistent inclusion of the interaction with the radiation field provides the time evolution of the wavefunction with both structural interaction (which ensures the bound state) and electromagnetic interaction. It is shown that in a short time after switching on the high-intensity radiation the bound charges are set free. In these conditions, a statistical criterion is used to estimate the rate of atom ionization. The results correspond to a sudden application of the electromagnetic interaction, in contrast with the well-known ionization probability obtained by quasi-classical tunneling through classically unavailable non-stationary states, or other equivalent methods, where the interaction is introduced adiabatically. For low-intensity radiation the charges oscillate and emit higher-order harmonics, the charge configuration is re-arranged and the process is resumed. Tunneling ionization may appear in these circumstances. Extension of the approach to other applications involving radiation-induced charge emission from bound states is discussed, like ionization of molecules, atomic clusters or proton emission from atomic nuclei. Also, results for a static electric field are included. [ABSTRACT FROM AUTHOR]

The cross-section is computed for non-relativistic charged particles (like electrons and ions) scattered by electromagnetic radiation confined to a finite region (like the focal region of optical laser beams). The cross-section exhibits maxima at scattering angles given by the energy and momentum conservation in multi-photon absorption or emission processes. For convenience, a potential scattering is included and a comparison is made with the wellknown Kroll-Watson scattering formula. The scattering process addressed in this paper is distinct from the process dealt with in previous studies, where the scattering is immersed in the radiation field. [ABSTRACT FROM AUTHOR]

Elastomers are frequently used in applications involving repeated impacts of hard abrasive particles on surfaces at high or moderate strain rates. Operational conditions of components experiencing erosive and impact type wear are sometimes difficult to mimic in laboratory conditions, and as such, it is common to approach behaviour and lifetime predictions by meticulously studying different types of single impacts. This is particularly true for characterising and modelling of high strain rate impact events between hard particles and a wearing elastomer surface. This work presents and applies such a methodology for two specific elastomer materials: a natural rubber (NR) and styrene–butadiene rubber (SBR) compounds. The elastomer materials are subjected to quasistatic and dynamic testing conditions for determination of hyper- and viscoelastic material properties. The results are used in an iterative calibration procedure for establishing related constitutive models by applying the Ogden and Prony series models. [ABSTRACT FROM AUTHOR]

The polarization of the vacuum under the action of an external classical field of electromagnetic radiation is investigated in the stationary regime. The electron-positron pairs interact both with the external field and with their own polarization field. For a macroscopic piece of vacuum the pairs are condensed on the low-momenta states and tend to form a quasi-localized electron-positron plasma of pairs, with single-particle states labeled by the position vector. In the polarization process under the action of a classical field of radiation the electron-positron and photon dynamics can be treated by means of classical fields. Under these circumstances, the corresponding coupled non-linear equations of motion are solved. It is shown that the pair dynamics consists of quasi-stationary single-particle states, while the polarization field reduces to a static magnetic field. The single-particle 'energy' (temporal phase) due to a monochromatic external field exhibits a spatial distribution characteristic of a stationary wave. Both the pair energy and the polarization energy are computed. Their values are extremely small, even for highly focused, reasonably high, external fields. The number of pairs is determined by the external energy. Under the action of a classical field the polarized vacuum is magnetized, and the corresponding (very low) magnetic susceptibility (the refractive index of the vacuum) is computed. [ABSTRACT FROM AUTHOR]

Abstract: The coherent interaction of the electromagnetic radiation with an ensemble of polarizable, identical particles with two energy levels is investigated in the presence of external electromagnetic fields. The coupled non-linear equations of motion are solved in the stationary regime and in the limit of small coupling constants. It is shown that an external electromagnetic field may induce a macroscopic occupation of both the energy levels of the particles and the corresponding photon states, governed by a long-range order of the quantum phases of the internal motion (polarization) of the particles. A lasing effect is thereby obtained, controlled by the external field. Its main characteristics are estimated for typical atomic matter and atomic nuclei. For atomic matter the effect may be considerable (for usual external fields), while for atomic nuclei the effect is extremely small (practically insignificant), due to the great disparity in the coupling constants. In the absence of the external field, the solution, which is non-analytic in the coupling constant, corresponds to a second-order phase transition (super-radiance), which was previously investigated. [ABSTRACT FROM AUTHOR]

The excitation spectrum of the density collective oscillations is computed for multi-component molecular mixtures with both Coulomb and (repulsive) short-range interactions. Distinct sound-like excitations appear, governed by the short-range interaction, which differ from the ordinary hydrodynamic sound. The dielectric function and the structure factor are also calculated. The 'two-sounds phenomenon' can be understood by means of the predictions of this model. [ABSTRACT FROM AUTHOR]

Abstract: The coupling of the electromagnetic field to matter polarization (dipole interaction) is examined in order to assess the possibility of setting up a coherent state as envisaged by Preparata and coworkers [G. Preparata, QED Coherence in Matter, World Scientific, 1995, and references therein]. It is found that coherence domains may set up in matter, their phases being arranged in a periodic lattice, as a consequence of, basically, a two-level interaction, which leads to a long-range ordered state, governed by a macroscopic occupation of both the photon state and the two levels. The non-linear equations of motion are solved for the new, non-perturbative ground-state, which is energetically favourable, provided the coupling strength exceeds a critical value. The elementary excitations with respect to this ground-state are derived, their energy being non-trivially affected by interaction. The “thermodynamics” of the coherent phase is computed and the super-radiant phase transition is re-derived in this context. Except for the general suggestion of coherence, the present results differ appreciably from Preparata''s, loc cit. [Copyright &y& Elsevier]

It is suggested that the dynamics of liquid water have a component consisting of O-2z (oxygen) anions and H+z (hydrogen) cations, where z is a (small) reduced effective electron charge. Such a model may apply to other similar liquids. The eigenmodes of density oscillations are derived for such a two-species ionic plasma, included the sound waves, and the dielectric function is calculated. The plasmons may contribute to the elementary excitations in a model introduced recently for the thermodynamics of liquids. It is shown that the sound anomaly in water can be understood on the basis of this model. The results are generalised to an asymmetric short-range interaction between the ionic species as well as to a multi-component plasma, and the structure factor is calculated. [ABSTRACT FROM AUTHOR]

As it is well known, a quantum system depending on parameters exhibits the (geometric) Berry phase when parameters are varying in the adiabatic limit. A generalization of the Berry phase is given in the present paper for a nonadiabatic change of parameters, which leads to quantum transitions in the system. This generalization is applied to noninertial motions and it is shown that such motions may induce quantum transitions for a system in an external field governed by Schrodinger's equation. [ABSTRACT FROM AUTHOR]

A model of phase transition of the first kind is introduced, based on the assumption that a classical gas of particles condenses in composite particles made up of various numbers of gas molecules. The transition temperature and the latent heat are derived, and the phase diagram is characterized. [ABSTRACT FROM AUTHOR]