Performance of the ATLAS Detector on First Single Beam and Cosmic Ray Data

We report on performance studies of the ATLAS detector obtained with first single LHC (Large Hadron Collider) beam data in September 2008, and large samples of cosmic ray events collected in the fall of 2008. In particular, the performance of the calorimeter, crucial for jet and missing transverse energy measurements, is studied. It is shown that the ATLAS experiment is ready to record the first LHC collisions.Comment: 4 pages, 6 figures, proceedings contribution of the SUSY 2009 conference in Bosto

Global Cardinality Constraints Make Approximating Some Max-2-CSPs Harder

Assuming the Unique Games Conjecture, we show that existing approximation algorithms for some Boolean Max-2-CSPs with cardinality constraints are optimal. In particular, we prove that Max-Cut with cardinality constraints is UG-hard to approximate within ~~0.858, and that Max-2-Sat with cardinality constraints is UG-hard to approximate within ~~0.929. In both cases, the previous best hardness results were the same as the hardness of the corresponding unconstrained Max-2-CSP (~~0.878 for Max-Cut, and ~~0.940 for Max-2-Sat). The hardness for Max-2-Sat applies to monotone Max-2-Sat instances, meaning that we also obtain tight inapproximability for the Max-k-Vertex-Cover problem

Competing SDW Phases and Quantum Oscillations in (TMTSF)2ClO4 in Magnetic Field

We propose a new approach for studying spin density waves (SDW) in the Bechgaard salt (TMTSF)2ClO4 where lattice is dimerized in transverse direction due to anion ordering. The SDW response is calculated in the matrix formulation that rigorously treats the hybridization of inter-band and intra-band SDW correlations. Since the dimerization gap is large, of the order of transverse bandwidth, we also develop an exact treatment of magnetic breakdown in the external magnetic field. The obtained results agree with the experimental data on the fast magneto-resistance oscillations. Experimentally found 260T rapid oscillations and the characteristic Tc dependance on magnetic field of relaxed material are fitted with our results for anion potential of the order of interchain hopping

Peierls-type structural phase transition in a crystal induced by magnetic breakdown

We predict a new type of phase transition in a quasi-two dimensional system of electrons at high magnetic fields, namely the stabilization of a density wave which transforms a two dimensional open Fermi surface into a periodic chain of large pockets with small distances between them. The quantum tunneling of electrons between the neighboring closed orbits enveloping these pockets transforms the electron spectrum into a set of extremely narrow energy bands and gaps which decreases the total electron energy, thus leading to a magnetic breakdown induced density wave (MBIDW) ground state. We show that this DW instability has some qualitatively different properties in comparison to analogous DW instabilities of Peierls type. E. g. the critical temperature of the MBIDW phase transition arises and disappears in a peculiar way with a change of the inverse magnetic field

Effects of transverse electron dispersion on photo-emission spectra of quasi-one-dimensional systems

The random phase approximation (RPA) spectral function of the one-dimensional electron band with the three-dimensional long range Coulomb interaction shows a broad feature which is spread on the scale of the plasmon energy and vanishes at the chemical potential. The fact that there are no quasi-particle $\delta$-peaks is the direct consequence of the acoustic nature of the collective plasmon mode. This behaviour of the spectral function is in the qualitative agreement with the angle resolved photo-emission spectra of some Bechgaard salts. In the present work we consider the modifications in the spectral function due to finite transverse electron dispersion. The transverse bandwidth is responsible for the appearance of an optical gap in the long wavelength plasmon mode. The plasmon dispersion of such kind introduces the quasi-particle $\delta$-peak into the spectral function at the chemical potential. The cross-over from the Fermi liquid to the non-Fermi liquid regime by decreasing the transverse bandwidth takes place through the decrease of the quasi-particle weight as the optical gap in the long wavelength plasmon mode is closing.Comment: 2 pages, 2 figures, ISCOM'0

The Role of Hydrophilic Sandblasted Titanium and Laser Microgrooved Zirconia Surfaces in Dental Implant Treatment

Dental implant surface modifications affect surface roughness, chemistry, topography, and consequently influence biological bone response. Current surface treatments are directed toward increased hydrophilicity and wettability of dental surfaces that allow earlier implant loading due to accelerated osseointegration. This is clinically reflected in increased implant stability and mainteined crestal bone level. Further modification includes microgrooving of zirconia implants by femtosecond laser ablation. Favorable initial results encourage further clinical assessment of this microgrooved zirconia implants

Микроструктурна адаптација коштаног ткива фацијалног скелета на дистрибуцију оклузалног оптерећења код особа са пуним зубним низом и њена улога у настанку прелома фацијалног скелета

Occlusal forces have traditionally been explained to transfer through the facial skeleton along specific osseous trajectories known as buttresses. These regions were assumed as zones of strength due to their thick cortical bone structure, while the areas between the buttresses containing thin cortical bone were considered weak and fragile. However, recent studies revealed that both cortical and trabecular bone of the mid-facial skeleton of dentulous individuals exhibit remarkable regional variations in structure and elastic properties. These variations have been frequently suggested to result from the different involvement of cortical and trabecular bone in the transfer of occlusal forces, although there has been no study to link bone microarchitecture to the occlusal loading. Moreover, although the classical concept of buttresses has been extensively studied by mechanical methods, such as finite element (FE) analysis, there is still no direct evidence for occlusal load distribution through the cortical and trabecular bone compartments individually. Additionally, relatively less scientific attention has been paid to the investigation of bone structure along Le Fort fracture lines that have traditionally been assumed as weak areas at which the mid-facial skeleton commonly fractures after injury. Papers published so far in this field focused mainly on the epidemiology and the role of injury mechanism in the fracture development, without considering the structural basis of increased bone fragility along the Le Fort fracture lines...Према традиционалном објашњeњу, пренос оклузалног оптерећења кроз кости лица током жвакања обавља се дуж специфичних путања унутар кости званих трајекторије или „батреси“. Ови делови костију лица сматрани су јаким зонама јер их изграђује кортикална кост велике дебљине, док су делови кости смештени између трајекторија сматрани слабим и фрагилним због њихове танке кортикалне грађе. Међутим, недавним истраживањима је откривено да и кортикална и трабекуларна кост средњег масива лица код особа са пуним зубним низом показују значајне регионалне варијације у грађи и еластичним својствима. Ове се варијације често сматрају адаптацијом кортикалне и трабекуларне кости на различито оптерећење у преносу оклузалних сила током жвакања, иако повезаност микроархитектуре кости и оклузалног оптерећења до сада није испитивана код људи. Штавише, иако је класични концепт преноса оклузалног оптерећења дуж трајекторија интензивно проучаван механичким методама, као што је метод коначних елемената, још увек није испитано на који начин се оклузалне силе преносе појединачно кроз кортикалну и трабекуларну кост. Значајно мању научну пажњу је привлачило испитивање грађе костију лица дуж Le Fort линија које су традиционално сматране најчешћим местима прелома костију фацијалног скелета узрокованих механичким силама. Досадашње студије у овој области су биле фокусиране углавном на епидемиолошка истраживања и улогу механизма повреде у настанку ових прелома, док структурна основа повећане фрагилности кости дуж Le Fort линија није испитивана..