Trajectory-based interpretation of laser light diffraction by a sharp edge

In the diffraction pattern produced by a half-plane sharp edge when it obstructs the passage of a laser beam, two characteristic regions are noticeable. There is a central region, where it can be noticed the diffraction of laser light in the region of geometric shadow, while intensity oscillations are observed in the non-obstructed area. On both sides of the edge, there are also very long light traces along the normal to the edge of the obstacle. The theoretical explanation to this phenomenon is based on the Fresnel-Kirchhoff diffraction theory applied to the Gaussian beam propagation behind the obstacle. Here we have supplemented this explanation by considering electromagnetic flow lines, which provide a more complete interpretation of the phenomenon in terms of electric and magnetic fields and flux lines, and that can be related, at the same time, with average photon paths.Comment: 13 pages, 5 figure

Fine Structure in Energy Spectra of Ultrasmall Au Nanoparticles

We have studied tunneling into individual Au nanoparticles of estimated diameters 2-5 nm, at dilution refrigerator temperatures. The I-V curves indicate resonant tunneling via discrete energy levels of the particle. Unlike previously studied normal metal particles of Au and Al, in these samples we find that the lowest energy tunneling resonances are split into clusters of 2-10 subresonances. Such effects appear to be increasingly important in smaller grains, as might be expected from the larger characteristic energies.Comment: 1 pdf fil

On Wheeler's delayed-choice Gedankenexperiment and its laboratory realization

Here, we present an analysis and interpretation of the experiment performed by Jacques et al. (2007 Science 315, 966), which represents a realization of Wheeler's delayed-choice Gedankenexperiment. Our analysis is based on the evolution of the photon state, since the photon enters into the Mach-Zehnder interferometer with a removable beam-splitter until it exits. Given the same incident photon state onto the output beam-splitter, BS_output, the photon's state at the exit will be very different depending on whether BS_output is on or off. Hence, the statistics of photon counts collected by the two detectors, positioned along orthogonal directions at the exit of the interferometer, is also going to be very different in either case. Therefore, it is not that the choice of inserting (on) or removing (off) a beam-splitter leads to a delayed influence on the photon behavior before arriving at the beam-splitter, but that such a choice influences the photon state at and after BS_output, i.e., after it has exited from the Mach-Zehnder interferometer. The random on/off choice at BS_output has no delayed effect on the photon to behave as a wave or a corpuscle at the entrance and inside the interferometer, but influences the subsequent evolution of the photon state incident onto BS_output.Comment: 7 pages, 4 figure

Transport in Graphene Tunnel Junctions

We present a technique to fabricate tunnel junctions between graphene and Al and Cu, with a Si back gate, as well as a simple theory of tunneling between a metal and graphene. We map the differential conductance of our junctions versus probe and back gate voltage, and observe fluctuations in the conductance that are directly related to the graphene density of states. The conventional strong-suppression of the conductance at the graphene Dirac point can not be clearly demonstrated, but a more robust signature of the Dirac point is found: the inflection in the conductance map caused by the electrostatic gating of graphene by the tunnel probe. We present numerical simulations of our conductance maps, confirming the measurement results. In addition, Al causes strong n-doping of graphene, Cu causes a moderate p-doping, and in high resistance junctions, phonon resonances are observed, as in STM studies.Comment: 22 pages, 5 figure

Applying OOC Techniques in the Reduction to Condensed Form for Very Large Symmetric Eigenproblems on GPUs

In this paper we address the reduction of a dense matrix to tridiagonal form for the solution of symmetric eigenvalue problems on a graphics processor (GPU) when the data is too large to fit into the accelerator memory. We apply out-of-core techniques to a three-stage algorithm, carefully redesigning the first stage to reduce the number of data transfers between the CPU and GPU memory spaces, maintain the memory requirements on the GPU within limits, and ensure high performance by featuring a high ratio between computation and communication

Coherence loss and revivals in atomic interferometry: A quantum-recoil analysis

The coherence effects induced by external photons coupled to matter waves inside a MachZehnder three-grating interferometer are analyzed. Alternatively to atomphoton entanglement scenarios, the model considered here only relies on the atomic wavefunction and the momentum shift induced in it by the photon scattering events. A functional dependence is thus found between the observables, namely the fringe visibility and the phase shift, and the transversal momentum transfer distribution. Good quantitative agreement is found when comparing the results obtained from our model with the experimental data. © 2012 IOP Publishing Ltd.MD, MB and DA acknowledge support from the Ministry of Science of Serbia under Projects OI171005, OI171028 and III45016. ASS acknowledges support from the Ministerio de Econom´ıa y Competitividad (Spain) under Projects FIS2010-22082 and FIS2010-29596-C02-01, as well as for a “Ram´on y Cajal” Research Fellowship.Peer Reviewe

Analysis of the p53 gene mutation status and methylation status of the promoters of p14 and p16 genes in liposarcoma

Липосаркоми, тумори мезенхималног порекла, представљају најучесталији хистолошки тип саркома меких ткива. Групу карактерише велика разноликост како у погледу патохистолошке организације тумора тако и биологије понашања. Уобичајена подела липосаркома обухвата следећа три подтипа: а.) добро диферентовани / дедиферентовани, б.) миксоидни / округлоћелијски и в.) плеоморфни. С обзиром на значајне клиничко-патолошке разлике између три подтипа липосаркома, вероватно је да су различити механизми укључени у њихов настанак и развој. На основу студија које су се фокусирале на истраживање генетике саркома меких ткива и костију, може се закључити да сигнални путеви p53-p14 и Rb-p16 играју одређену улогу у свим типовима саркома. Разјашњавање улоге ових сигналних путева у патогенези липосаркома, може да буде допринос како дијагностици и прогностици липосаркома, тако и дефинисању потенцијалних терапеутских циљева. Студија је обухватила испитивање мутационог статуса гена р53 и метилационог статуса гена р14 и р16, на 33 узорка липосаркома, сва три подтипа. У циљу свеобухватније анализе испитивана је и експресија протеина р16, циклина D1 и фактора пролиферације Ki-67, применом имунохистохемијског бојења. Резултати експеримента су показали да промене у сигналним путевима р53-р14 и р16-Rb могу имати значаја у патогенези сва три подтипа липосаркома. Разлике се огледају у квалитету и квантитету промена.Liposarcoma, tumors of mesenchymal origin, represent the most frequent type of soft tissue sarcomas. The group is characterized by a great diversity regarding pathohistology and biological behavior. The group can be divided into three different subtypes: a.) well differentiated / dedifferentiated, b.) myxoid / round cell and c.) pleomorphic. Given the significant clinical and pathological differences between the three subtypes of liposarcoma, it is likely that different mechanisms are involved in their formation and development. Based on the studies that have been focused on genetic research of sarcoma of soft tissues and bones, conclusion can be drawn that the p53-p14 and Rb-p16 signaling pathways play a certain role in sarcomagenesis. Clarification of the role of these signaling pathways in the pathogenesis of liposarcoma, could be a contribution towards better diagnostic and prognostic criteria and the identification of potential therapeutic targets. The study included examination of the p53 gene mutation status and assessment of the p14/p16 gene methylation status in 33 liposarcoma samples of all three subtypes. For the purpose of more comprehensive analysis, protein expression of the p16, cyclin D1 and Ki-67 has been evaluated by immunohistochemical staining. The results of the study have showed that the alterations of the targeted signal pathways are important in the pathogenesis of all three subtypes of liposarcoma. The differences are reflected in the quality and quantity of the detected alterations

Mesoscopic Resistance Fluctuations in Cobalt Nanoparticles

We present measurements of mesoscopic resistance fluctuations in cobalt nanoparticles and study how the fluctuations with bias voltage, bias fingerprints, respond to magnetization reversal processes. Bias fingerprints rearrange when domains are nucleated or annihilated. The domain-wall causes an electron wavefunction phase-shift of $\approx 5\pi$. The phase-shift is not caused by the Aharonov-Bohm effect; we explain how it arises from the mistracking effect, where electron spins lag in orientation with respect to the moments inside the domain-wall. Dephasing time in Co at $0.03K$ is short, $\tau_\phi\sim ps$, which we attribute to the strong magnetocrystalline anisotropy.Comment: 5 pages 3 figs colou

Spectroscopy, Interactions and Level Splittings in Au Nanoparticles

We have measured the electronic energy spectra of nm-scale Au particles using a new tunneling spectroscopy configuration. The particle diameters ranged from 5nm to 9nm, and at low energies the spectrum is discrete, as expected by the electron-in-a-box model. The density of tunneling resonances increases rapidly with energy, and at higher energies the resonances overlap forming broad resonances. Near the Thouless energy, the broad resonances merge into a continuum. The tunneling resonances display Zeeman splitting in a magnetic field. Surprisingly, the g-factors (~0.3) of energy levels in Au nano-particles are much smaller than the g-factor (2.1) in bulk gold

Effect of muscular training on urinary 17-ketosteroids

Promene u izlučivanju 17-ketosteroida mokraćom nastale pod uticajem kratkotrajnog intenzivnog mišićnog napora u toku treninga nisu još uvijek jasne niti su dovoljno proučene. Proučavali smo ovaj problem na netreniranim klinički zdravim studentima-dobrovoljcima, životne dobi od 20 do 22 godine u uslovima svakodnevnog mišićnog treninga za vreme 13 dana, i to pre i posle rada i u toku oporavka 5 sati posle rada. Određivanje 17-ketosteroida u mokraći vršeno je kvantitativno Zimmermannovom reakcijom u sopstvenoj modifikaciji. Vežba na bicikl-ergometru po Mülleru obavljena je svakog dana u 8 časova pre podne uz opterećenje od 150 mkg/min, a ukupno maksimalno opterećenje iznosilo je 18000 mkg u 12 minuta rada. Sve zdrave osobe nisu podnele ovo opterećenje, pa su u ogledu zadržane samo one osobe koje su ovu veoma napornu vežbu izdržale dokraja. Postignuti rezultati prikazani su tablicom i grafikonima. Nađeno je da postoji razlika između srednjih vrednosti 17-ketosteroida pre i posle mišićnog naprezanja te konstatovano da kod netreniranih osoba mišićni rad izaziva kratkotrajan porast izlučivanja 17-ketosteroida. Ovaj efekat bio je najjače izražen prvog dana treniranja, narednih dana bio je manji, a na kraju trinaestodnevnog perioda treniranja potpuno se izgubio. U oporavku - mirovanju 5 časova posle vežbe - vrednosti 17-ketosteroida bile su niže nego pre rada. Ovaj pozni efekt mišićne vežbe na izlučivanje 17-ketosteroida s mokraćom u saglasnosti je s rezultatima naših ranijih ispitivanja koja su pokazala da nekoliko časova posle mišićnog naprezanja nastupa faza u kojoj je izlučivanje 17-ketosteroida snižene. Međutim, nije se moglo uočiti da treniranje utiče u smislu izmene ovog poznog efekta mišićnog rada na izlučivanje 17-ketosteroida.The changes in the elimination of 17-ketosteroids in the urine due to short-lasting intense muscular work in the course of training have not yet been fully explained. The problem was studied in untrained healthy students-volunteers aged 20-22 in conditions of everyday muscular work, for 13 days, before and after the exercise as well as during restitution 5 hours after the cessation of work. The determination of 17-ketosteroids in urine was carried out quantitatively using own modification of the Zimmermann reaction. The exercise on the Muller\u27s bicycle ergometer was performed every day at 8 a. m, with a Ioad of 1500 mkg/min, while the total maximal load was 18.000 kgm for a 12-minute work. All healthy subjects were not able to endure the load, so that only those who accomplished this very strenuous exercise, remained in the experiment. The results are shown in tables and graphs. A difference was found in the mean 17-ketosteroid values before and after muscular effort. In untrained persons muscular effort induced a short increase in the 17-ketosteroid elimination. This effect was most marked the first day of training, it was Iess the following days, and completely disappeared at the end of the 13-day period. During restitution (a 5-hour rest after work) the urinary 17-ketosteroid values were lower than before work. This late effect of muscular effort on the elimination of 17-ketosteroids in urine was in agreement with the results of the authors earlier Investigations which had shown that a few hours after the muscular effort the 17-ketosteroid elimination is diminished. The training was not found to produce any changes in this late effect of muscular work on the 17-ketosteroid elimination