The single-particle density matrix and the momentum distribution of dark "solitons" in a Tonks-Girardeau gas

We study the reduced single-particle density matrix (RSPDM), the momentum distribution, natural orbitals and their occupancies, of dark "soliton" (DS) states in a Tonks-Girardeau gas. DS states are specially tailored excited many-body eigenstates, which have a dark solitonic notch in their single-particle density. The momentum distribution of DS states has a characteristic shape with two sharp spikes. We find that the two spikes arise due to the high degree of correlation observed within the RSPDM between the mirror points ($x$ and $-x$) with respect to the dark notch at $x=0$; the correlations oscillate rather than decay as the points $x$ and $-x$ are being separated.Comment: 9 pages, 8 figure

Procena usamljenosti studenata sa oštećenjem vida

Background/Aim. Loneliness is becoming more frequent, especially in young people. Some authors believe that visual impairments increase the risk of loneliness. Empirical data on its manifestation in persons with visual impairments are contradictory. The aim of this research was to determine the degree of loneliness in students with visual impairments and their peers from general population. Methods. A comparative research was conducted on a sample consisting of 36 visually impaired students and 101 students without visual impairments (control group). Students with visual impairments were divided into 3 subgroups with regard to the degree of visual impairments (students with low vision, legally blind, and totally blind students). University of California Los Angeles Loneliness Scale (which assesses the general loneliness) and Social and Emotional Loneliness Scale (which assesses social loneliness, family loneliness, and romantic loneliness) were used in our investigation. Results. The results showed that the general loneliness was significantly lower in the group of students with visual impairments than in the control group (t = 2.121; p = 0.036). There were no significant differences in the Social and Emotional Loneliness Scale between the group with visual impairments and the control group. No significant differences were determined in the level of loneliness among students with a different degree of visual impairments. There are significant differences in the manifestation level of social loneliness, family loneliness, and romantic loneliness (Wilk's lambda = 0.604; p ≤ 0.000) in the group of students with visual impairments. Romantic loneliness was manifested the most, followed by social loneliness, while family loneliness was the least manifested. Conclusion. With regard to the results of our research, visual impairment alone is not a crucial factor of loneliness in students with visual impairments. Further studies on protective factors of loneliness can contribute to its prevention in young people with visual impairments.Uvod/Cilj. Usamljenost je sve učestalija, posebno u populaciji mladih. Neki autori smatraju da oštećenje vida povećava rizik od usamljenosti. Empirijski podaci o ispoljenosti kod osoba sa oštećenjem vida su kontradiktorni. Cilj našeg istraživanja bio je utvrđivanje stepena usamljenosti kod studenata sa oštećenjem vida i njihovih vršnjaka iz opšte populacije. Metode. Komparativno istraživanje je obavljeno na uzorku koji je činilo 36 studenata sa oštećenjem vida i 101 studenata bez oštećenja vida (kontrolna grupa). Na osnovu stepena oštećenja vida, studenti sa oštećenjem vida bili su podeljeni u tri podgrupe (slabovidi, praktično slepi i potpuno slepi). U našem istraživanju korišćeni su University of California Los Angeles Loneliness Scale (za procenu opšte usamljenosti) i Skala socijalne i emocionalne usamljenosti (za procenu socijalne, porodične i usamljenosti u ljubavi). Rezultati. Analiza rezultata je pokazala da je opšta usamljenost bila značajno manja u grupi studenata sa oštećenjem vida nego u kontrolnoj grupi (t = 2.121; p = 0.036). Na Skali socijalne i emocionalne usamljenosti nije utvrđena statistički značajna razlika između grupe studenata sa oštećenjem vida i kontrolne grupe. Takođe, nije utvrđena značajna razlika u nivou usamljenosti između studenata sa različitim stepenom oštećenja vida. U grupi studenata sa oštećenjem vida postojala je značajna razlika u stepenu ispoljenosti socijalne usamljenosti, usamljenosti u porodici i usamljenosti u ljubavi (Wilk's lambda = 0.604; p ≤ 0.000). Najviše je bilo ispoljena usamljenost u ljubavi, sledi socijalna usamljenost, dok je usamljenost u porodici bila najmanja. Zaključak. Prema rezultatima našeg istraživanja, samo oštećenje vida nije presudni činilac usamljenosti kod studenata sa oštećenjem vida. Buduća istraživanja protektivnih faktora usamljenosti mogu doprineti prevenciji ove pojave kod mladih sa oštećenjem vida

About loach in the Sava river

Porodica Cobitidae obuhvaća otprilike 160 vrsta, no rod Cobitis je još uvijek nedovoljno proučen. U rijeci Savi u blizini Zagreba zabilježene su dvije vrste iz roda Cobitis, C. elongata i C. elongatoides. Obje vrste žive na istom staništu u muljevitim i sporotekućim dijelovima rijeke. Nije pronađen niti jedan podatak literature o njihovoj biologiji pa su stoga su ciljevi ovog istraživanja bili utvrditi uvjete rasta vijuna iz gornjeg toka rijeke Save. Prikupljanje uzoraka vode, makrozoobentosa i riba izvršeno je 15. svibnja 2006. na lokaciji Medsave i 17. svibnja 2006. na lokacijama Lijevi Dubrovčak i Setuš. Kvaliteta vode rijeke Save pogodna je za rast, razmnožavanje i život C. elongata, a manje za C. elongatoides. Makrozoobentos je zastupljen sa 10 taksona na sve tri lokacije, a od toga na lokaciji Medsave najviše su zastupljeni Crustacea, na lokaciji Lijevi Dubrovčak Oligochaeta, a na lokaciji Setuš Diptera i Gastropoda. Morfometrijske vrijednosti pokazuju određena odstupanja uvjetovana razlikama u dimenzijama tijela ovih dviju vrsta vijuna. Izmjerene vrijednosti smještaja početka i kraja prsne peraje, te početka trbušne peraje na tijelu obje vrste vijuna najviše su se i razlikovale od ostalih izmjera. Faktor kondicije ukazuje da C. elongatoides ima veću tjelesnu masu, te da je bolje uhranjen, budući da njegov CF iznosi 0,81, dok kod C. elongata iznosi 0,61. Rezultati dužinsko masenih odnosa C. elongata mogu se prikazati formulom W= 0,0039 * SL3,2063, a C. elongatoides W= 0,0057 * SL 3,1872.Cobitidae family contains cca 160 species but there isn\u27t enough data on the genus Cobitis. In the Sava river near Zagreb, two species of the genus Cobitis were recorded C. elongata and C. elongatoides. Both species live together in the mud covered slow flowing sections of the river. As no data on the biology of these two loach were found in literature, the aim of this study was to research the conditions of the loach from the Sava river. The fish were caught by electric gear on three locations in May 2006. Also, macroinvertebrates were collected and physical and chemical analyses of water were performed. Quality of water of the Sava river is sufficient for growth, reproduction and presence of C. elongata, it is less so for C. elongatoides. Macroinvertebrates are present with 10 taxa at three investigated sites. Crustacea was dominant at Medsave site, Oligochaeta at Lijevi Dubrovčak site and Diptera and Gastropoda at Setuš site. There are some differences in morphometric parameters of both species, due to the differences in the body dimensions. Main differences occurred when measuring the value of prepectoral distance, the end of prepectoral distance and preventral distance of the fin. Condition factor of C elongata was lower (0,61) than that of C. elongatoides (0,81). Length-mass relationships of C. elongata could be expressed by the following formula: W= 0,0039 * SL3,2063, and C. elongatoides W= 0,0057 * SL 3,187

Near-field thermal radiation transfer controlled by plasmons in graphene

It is shown that thermally excited plasmon-polariton modes can strongly mediate, enhance and \emph{tune} the near-field radiation transfer between two closely separated graphene sheets. The dependence of near-field heat exchange on doping and electron relaxation time is analyzed in the near infra-red within the framework of fluctuational electrodynamics. The dominant contribution to heat transfer can be controlled to arise from either interband or intraband processes. We predict maximum transfer at low doping and for plasmons in two graphene sheets in resonance, with orders-of-magnitude enhancement (e.g. $10^2$ to $10^3$ for separations between $0.1\mu m$ to $10nm$) over the Stefan-Boltzmann law, known as the far field limit. Strong, tunable, near-field transfer offers the promise of an externally controllable thermal switch as well as a novel hybrid graphene-graphene thermoelectric/thermophotovoltaic energy conversion platform.Comment: 4 pages, 3 figure

Mid-infrared plasmons in scaled graphene nanostructures

Plasmonics takes advantage of the collective response of electrons to electromagnetic waves, enabling dramatic scaling of optical devices beyond the diffraction limit. Here, we demonstrate the mid-infrared (4 to 15 microns) plasmons in deeply scaled graphene nanostructures down to 50 nm, more than 100 times smaller than the on-resonance light wavelength in free space. We reveal, for the first time, the crucial damping channels of graphene plasmons via its intrinsic optical phonons and scattering from the edges. A plasmon lifetime of 20 femto-seconds and smaller is observed, when damping through the emission of an optical phonon is allowed. Furthermore, the surface polar phonons in SiO2 substrate underneath the graphene nanostructures lead to a significantly modified plasmon dispersion and damping, in contrast to a non-polar diamond-like-carbon (DLC) substrate. Much reduced damping is realized when the plasmon resonance frequencies are close to the polar phonon frequencies. Our study paves the way for applications of graphene in plasmonic waveguides, modulators and detectors in an unprecedentedly broad wavelength range from sub-terahertz to mid-infrared.Comment: submitte

Tunable hybrid surface waves supported by a graphene layer

We study surface waves localized near a surface of a semi-infinite dielectric medium covered by a layer of graphene in the presence of a strong external magnetic field. We demonstrate that both TE-TM hybrid surface plasmons can propagate along the graphene surface. We analyze the effect of the Hall conductivity on the disper- sion of hybrid surface waves and suggest a possibility to tune the plasmon dispersion by the magnetic field.Comment: 3 pages, 3 figure

Graphene-based photovoltaic cells for near-field thermal energy conversion

Thermophotovoltaic devices are energy-conversion systems generating an electric current from the thermal photons radiated by a hot body. In far field, the efficiency of these systems is limited by the thermodynamic Schockley-Queisser limit corresponding to the case where the source is a black body. On the other hand, in near field, the heat flux which can be transferred to a photovoltaic cell can be several orders of magnitude larger because of the contribution of evanescent photons. This is particularly true when the source supports surface polaritons. Unfortunately, in the infrared where these systems operate, the mismatch between the surface-mode frequency and the semiconductor gap reduces drastically the potential of this technology. Here we show that graphene-based hybrid photovoltaic cells can significantly enhance the generated power paving the way to a promising technology for an intensive production of electricity from waste heat.Comment: 5 pages, 4 figure

Intrinsic Terahertz Plasmons and Magnetoplasmons in Large Scale Monolayer Graphene

We show that in graphene epitaxially grown on SiC the Drude absorption is transformed into a strong terahertz plasmonic peak due to natural nanoscale inhomogeneities, such as substrate terraces and wrinkles. The excitation of the plasmon modifies dramatically the magneto-optical response and in particular the Faraday rotation. This makes graphene a unique playground for plasmon-controlled magneto-optical phenomena thanks to a cyclotron mass 2 orders of magnitude smaller than in conventional plasmonic materials such as noble metals.Comment: to appear in Nano Letter

Real-space mapping of tailored sheet and edge plasmons in graphene nanoresonators

Plasmons in graphene nanoresonators have many potential applications in photonics and optoelectronics, including room-temperature infrared and terahertz photodetectors, sensors, reflect arrays or modulators1, 2, 3, 4, 5, 6, 7. The development of efficient devices will critically depend on precise knowledge and control of the plasmonic modes. Here, we use near-field microscopy8, 9, 10, 11 between λ0 = 10–12 μm to excite and image plasmons in tailored disk and rectangular graphene nanoresonators, and observe a rich variety of coexisting Fabry–Perot modes. Disentangling them by a theoretical analysis allows the identification of sheet and edge plasmons, the latter exhibiting mode volumes as small as 10−8λ03. By measuring the dispersion of the edge plasmons we corroborate their superior confinement compared with sheet plasmons, which among others could be applied for efficient 1D coupling of quantum emitters12. Our understanding of graphene plasmon images is a key to unprecedented in-depth analysis and verification of plasmonic functionalities in future flatland technologies.Peer ReviewedPostprint (author's final draft

Resonant Visible Light Modulation with Graphene

Fast modulation and switching of light at visible and near-infrared (vis-NIR) frequencies is of utmost importance for optical signal processing and sensing technologies. No fundamental limit appears to prevent us from designing wavelength-sized devices capable of controlling the light phase and intensity at gigaherts (and even terahertz) speeds in those spectral ranges. However, this problem remains largely unsolved, despite recent advances in the use of quantum wells and phase-change materials for that purpose. Here, we explore an alternative solution based upon the remarkable electro-optical properties of graphene. In particular, we predict unity-order changes in the transmission and absorption of vis-NIR light produced upon electrical doping of graphene sheets coupled to realistically engineered optical cavities. The light intensity is enhanced at the graphene plane, and so is its absorption, which can be switched and modulated via Pauli blocking through varying the level of doping. Specifically, we explore dielectric planar cavities operating under either tunneling or Fabry-Perot resonant transmission conditions, as well as Mie modes in silicon nanospheres and lattice resonances in metal particle arrays. Our simulations reveal absolute variations in transmission exceeding 90% as well as an extinction ratio >15 dB with small insertion losses using feasible material parameters, thus supporting the application of graphene in fast electro-optics at vis-NIR frequencies.Comment: 17 pages, 13 figures, 54 reference