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Search Results: 1 - 10 of 29197 matches for " Cristina Simon "
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Dirac point metamorphosis from third-neighbor couplings in graphene
Cristina Bena,Laurent Simon
Physics , 2010, DOI: 10.1103/PhysRevB.83.115404
Abstract: We study the band structure and the density of states of graphene in the presence of a next-to-nearest-neighbor coupling (N2) and a third-nearest-neighbor coupling (N3). We show that for values of N3 larger or equal to 1/3 of the value of the nearest-neighbor hopping (NN), extra Dirac points appear in the spectrum. If N3 is exactly equal to 1/3 NN, the new Dirac points are localized at the M points of the Brillouin zone and are hybrid: the electrons have a linear dispersion along the GammaM direction and a quadratic dispersion along the perpendicular direction MK. For larger values of N3 the new points have a linear dispersion, and are situated along the MK line. For a value of N3 equal to 1/2 NN, these points merge with the Dirac cones at the K points, yielding a gapless quadratic dispersion around K, while for larger values each quadratic point at K splits again into four Dirac points. The effects of changing the N2 coupling are not so dramatic. We calculate the density of states and we show that increasing the N3 coupling lowers the energy of the Van Hove singularities, and when N3 is larger than 1/3 NN the Van Hove singularities split in two, giving rise to extra singularities at low energies.
Romanian Tourism Facing Labour Shortage
Cristina Simon,Dan Popescu,Iulia Chivu
Acta Universitatis Danubius : Oeconomica , 2008,
Abstract: The purpose of this paper is to present the main tendencies in the Romanian tourism and their impact on the labour market. The first partof the paper presents the main tendencies in travel and tourism sector. The second part of the paper focuses on the challenges of the labour market inthe hotel sector, highlighting essential aspect related to the declining of population, shortage of the workforce, emigration, financial compensations.The final part exposes few ideas and possible suggestions that can be applied into the travel and tourism sector in order to better manage the multipledimensions of growth.
Spin and Majorana polarization in topological superconducting wires
Doru Sticlet,Cristina Bena,Pascal Simon
Physics , 2011, DOI: 10.1103/PhysRevLett.108.096802
Abstract: We study a one-dimensional wire with strong Rashba and Dresselhaus spin-orbit coupling (SOC), which supports Majorana fermions when subject to a Zeeman magnetic field and in proximity of a superconductor. Using both analytical and numerical techniques we calculate the electronic spin texture of the Majorana end states. We find that the spin polarization of these states depends on the relative magnitude of the Rashba and Dresselhaus SOC components. Moreover, we define and calculate a local "Majorana polarization" and "Majorana density" and argue that they can be used as order parameters to characterize the topological transition between the trivial system and the system exhibiting Majorana bound modes. We find that the local "Majorana polarization" is correlated to the transverse spin polarization, and we propose to test the presence of Majorana fermions in a 1D system by a spin-polarized density of states measurement.
Characterizing p-wave superconductivity using the spin structure of Shiba states
Vardan Kaladzhyan,Cristina Bena,Pascal Simon
Physics , 2015,
Abstract: We study the formation of Shiba states in two-dimensional superconductors with broken inversion symmetry where the order parameter consists of a mixture of s-wave and p-wave. We find important differences between the spin polarization of the Shiba states between the s-wave and p-wave dominated phases, both for the total polarization and for its spatial structure. Such signatures, which could be obtained using spin-polarized STM, allow to unambiguously discriminate between these phases and also to determine the direction of the spin-triplet pairing vector with respect to the sample plane.
Spectral properties of Luttinger liquids: A comparative analysis of regular, helical, and spiral Luttinger liquids
Bernd Braunecker,Cristina Bena,Pascal Simon
Physics , 2011, DOI: 10.1103/PhysRevB.85.035136
Abstract: We provide analytic expressions for the Green's functions in position-frequency space as well as for the tunneling density of states of various Luttinger liquids at zero temperature: the standard spinless and spinful Luttinger liquids, the helical Luttinger liquid at the edge of a topological insulator, and the Luttinger liquid that appears either together with an ordering transition of nuclear spins in a one-dimensional conductor, or in spin-orbit split quantum wires in an external magnetic field. The latter system is often used to mimic a helical Luttinger liquid, yet we show here that it exhibits significantly different response functions and, to discriminate, we call it the spiral Luttinger liquid. We give fully analytic results for the tunneling density of state of all the Luttinger liquids as well as for most of the Green's functions. The remaining Green's functions are expressed by simple convolution integrals between analytic results.
Josephson effect in superconducting wires supporting multiple Majorana edge states
Doru Sticlet,Cristina Bena,Pascal Simon
Physics , 2012, DOI: 10.1103/PhysRevB.87.104509
Abstract: We study superconducting-normal-superconducting (SNS) Josephson junctions in one-dimensional topological superconductors which support more than one Majorana end mode. The variation of the energy spectrum with the superconducting phase is investigated by combining numerical diagonalizations of tight-binding models describing the SNS junction together with an analysis of appropriate low-energy effective Hamiltonians. We show that the four pi-periodicity characteristic of the fractional dc Josephson effect is preserved. Additionally, the ideal conductance of a NS junction with a topological supraconductor, hosting two Majorana modes at its ends, is doubled compared to the single Majorana case. Last, we illustrate how a nonzero superconducting phase gradient can potentially destroy the phases supporting multiple Majorana end states.
The Role of Ultrasound and Air Leak Measurement in Assessing Lung Expansion after Thoracic Surgery  [PDF]
Abraham Chavarín, Laureano Molins, Jose M. Mier, Juan J. Fibla, Cristina Izquierdo-Vidal, Cristina Simon, Angela Guirao, Jorge Hernandez
Surgical Science (SS) , 2015, DOI: 10.4236/ss.2015.68052
Abstract: Objective: To determine if lung ultrasound semiology is applicable to the post-surgical hemithorax, and its value in the evaluation of lung expansion in the postoperative period when paired with the use of digital chest drain systems. Methods: Prospective observational study including all patients undergoing thoracic surgery from June 2012 to March 2013. Patients undergoing pleurodesis or hemodynamically unstable were not considered candidates. Final inclusion in the study was based on the availability of digital chest drain system. A transthoracic lung ultrasound evaluation of the anterior and anterolateral windows was performed 20 minutes after chest drain placement. Presence or not of lung sliding and air leak values taken from the digital chest drain system were recorded. Data were submitted to a binomial classification test for analysis. Results: Forty-nine patients were included, yielding a total of 64 hemithoraces. Lung sliding was seen in 53 cases (82.8%), and an air leak value of 20 ml/min or less in 56 cases (87.5%). Sensitivity was 92.8% (95% CI: 82.6% to 97.9%) and specificity 87.5% (95% CI: 47.3% to 97.9%). Positive predictive value was 98.1%, and negative predictive value was 63.6%. Conclusions: Transthoracic lung ultrasound is a useful technique that can complement the use of digital chest drain systems in the evaluation of post-surgical lung expansion. The incorporation of lung ultrasound can greatly reduce the need for chest radiographs in thoracic surgery departments.
Synthesis of Bis-ureas from Bis(o-nitrophenyl) Carbonate
Maria-Cristina Turoczi,Monika Simon,Valentin Badea,Carol Csunderlik
Molecules , 2008, DOI: 10.3390/molecules13123192
Abstract: A general method for the preparation of bis-ureas from bis(o-nitrophenyl) carbonate has been developed. Directional urea synthesis is achieved by sequential amine addition to bis(o-nitrophenyl) carbonate in two steps: in the first step bis(o-nitrophenyl) carbonate is reacted with benzylamine to form benzyl-o-nitrophenyl carbamate; in the second step the carbamate is reacted with a variety of diamines in toluene to yield bis-ureas.
Evidence of mingling between contrasting magmas in a deep plutonic environment: the example of Várzea Alegre, in the Ribeira Mobile Belt, Espírito Santo, Brazil
MEDEIROS, SILVIA R.;WIEDEMANN-LEONARDOS, CRISTINA M.;VRIEND, SIMON;
Anais da Academia Brasileira de Ciências , 2001, DOI: 10.1590/S0001-37652001000100009
Abstract: at the end of the geotectonic cycle that shaped the northern segment of the ribeira mobile belt (upper proterozoic to paleozoic age), a late to post-collisional set of plutonic complexes, consisting of a wide range of lithotypes, intruded all metamorphic units. the várzea alegre intrusive complex is a post-collisional complex. the younger intrusion consists of an inversely zoned multistage structure envolved by a large early emplaced ring of megaporphyritic charnoenderbitic rocks. the combination of field, petrographic and geochemical data reveals the presence of at least two different series of igneous rocks. the first originated from the partial melting of the mantle. this was previously enriched in incompatible elements, low and intermediate ree and some hfs-elements. a second enrichment in lree and incompatible elements in this series was due to the mingling with a crustal granitic magma. this mingling process changed the composition of the original tholeiitic magma towards a medium-k calc-alkalic magma to produce a suite of basic to intermediate rock types. the granitic magma from the second high-k, calc-alkalic suite originated from the partial melting of the continental crust, but with strong influence of mantle-derived melts.
Evidence of mingling between contrasting magmas in a deep plutonic environment: the example of Várzea Alegre, in the Ribeira Mobile Belt, Espírito Santo, Brazil
MEDEIROS SILVIA R.,WIEDEMANN-LEONARDOS CRISTINA M.,VRIEND SIMON
Anais da Academia Brasileira de Ciências , 2001,
Abstract: At the end of the geotectonic cycle that shaped the northern segment of the Ribeira Mobile Belt (Upper Proterozoic to Paleozoic age), a late to post-collisional set of plutonic complexes, consisting of a wide range of lithotypes, intruded all metamorphic units. The Várzea Alegre Intrusive Complex is a post-collisional complex. The younger intrusion consists of an inversely zoned multistage structure envolved by a large early emplaced ring of megaporphyritic charnoenderbitic rocks. The combination of field, petrographic and geochemical data reveals the presence of at least two different series of igneous rocks. The first originated from the partial melting of the mantle. This was previously enriched in incompatible elements, low and intermediate REE and some HFS-elements. A second enrichment in LREE and incompatible elements in this series was due to the mingling with a crustal granitic magma. This mingling process changed the composition of the original tholeiitic magma towards a medium-K calc-alkalic magma to produce a suite of basic to intermediate rock types. The granitic magma from the second high-K, calc-alkalic suite originated from the partial melting of the continental crust, but with strong influence of mantle-derived melts.
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