Discrete breathers in polyethylene chain

The existence of discrete breathers (DBs), or intrinsic localized modes (localized periodic oscillations of transzigzag) is shown. In the localization region periodic contraction-extension of valence C-C bonds occurs which is accompanied by decrease-increase of valence angles. It is shown that the breathers present in thermalized chain and their contribution dependent on temperature has been revealed.Comment: 5 pages, 6 figure

Three columns vertebrotomies in extra-apical area as a method of surgical deformity correction of cervicothoracic transition: analysis of the clinical series and literature data

Design: retrospective analysis of the clinical observations. Level of evidence – III. Aim: retrospective analysis of the treatment results of the patients with malformation and segmentation of the cervical and upper thoracic vertebrae. Materials and methods. Retrospective multi-center cohort of 8 cases aged from 8 to 15 years. Inclusive criteria are as follows: children aged less than 15 years by the time of operation, deformity in the frontal plane, application of three columns vertebrotomy and complete radiological archive availability. Results. Patients with multiple abnomalies with a leading component maldevelopment of vertebral segmentation and formation are predominated. There were no violations of sagittal balance in patients. The amount of scoliotic deformity according to Cobb ranged from 30 ° to 66 ° (mean value - 46.1 °), with a frontal imbalance in 6 (55,5%) patients. After operations scoliosis values were from 3 ° to 34 ° (mean value - 15.3 °). However in all cases after operation the frontal balance was restored. The amount of correction ranged from 49% to 90% (mean 69,4%). No permanent neurological complications were observed in peri- and post-operative periods. Conclusion. The key criterion for surgical correction of the defects of the cervicothoracic transition is the reconstruction of the local balance in the frontal and sagittal planes, and not the absolute correction of local deformation. Spine osteotomy in extra-apical area in children with multiple mal-developments of the cervical and upper thoracic spine allows us to produce adequate deformity correction (for mean 69,4%) and to reduce the risk of neurological disorders through main compression manipulation. That reduces the zone of instrumental fixation which is important for preservation of the axial growth

ХИРУРГИЧЕСКОЕ ЛЕЧЕНИЕ ДЕТЕЙ С НЕТРАВМАТИЧЕСКИМ ЗАСТАРЕЛЫМ АТЛАНТО-АКСИАЛЬНЫМ РОТАЦИОННЫМ БЛОКИРОВАНИЕМ

Atlanto-axial rotatory fixation (AORF) develops on the background of acute torticollis. Widely adopted terms such as C1 subluxation or atlantooccipital rotational subluxation do not reflect the core of this pathology and carry negative weight in the diagnostics and treatment of AORF. Retrospective analysis of the diagnostics and treatment outcome of 5 children with confirmed AORF diagnosis and literature review were performed. Clinical method, radiography and functional computer tomography were used to verify the diagnosis. De-rotational halo-traction and open correction with screw fixation were applied for treatment. Head position was managed to be improved in all patients. In one case the reduction was performed using correction in suboccipital segments and in other 4 cases the correction and fixation by Harms and de-rotational halo-traction allowed to correct torticollis. The pain syndrome had been arrested completely. Disease outcome resulted in formation of C1-C2 fibrous or bone fusion regardless the method of treatment. The patients with neglected AORF represent a great challenge for diagnostics and treatment. When conservative treatment fails it is necessary to involve de-rotational halo-traction with possible application of open reduction and posterior fusion. The purpose of treatment is to eliminate torticollis and pain using creation of proper C1-C2 alignment. The motions in atlantooccipital joint do not restore due to formation of the fibrous or bone fusion.Атланто-аксиальное ротационное блокирование (ААРБ) развивается на фоне синдрома острой кривошеи. Широко применяемые у нас термины «подвывих С1» или «атланто-аксиальный ротационный подвывих» не отражают сути данной патологии и вносят свою отрицательную лепту в диагностику и лечения ААРБ. Представлены ретроспективный анализ диагностики и результатов лечения 5 детей с подтвержденным диагнозом ААРБ, обзор литературы. Для подтверждения диагноза использовались клинический метод, рентгенография и функциональная компьютерная томография. В качестве методов лечения применялось деротационное halo-вытяжение, открытая коррекция с винтовой фиксацией. У всех пациентов удалось улучшить положение головы. В одном случае репозиция выполнена за счет коррекции в субаксиальных сегментах, у остальных 4 пациентов коррекция и фиксация по Harms и деротационное halo-вытяжение позволили устранить кривошею. Болевой синдром купирован полностью. Исходом заболевания вне зависимости от метода лечения являлось образование фиброзного или костного блока С1-С2. Пациенты с застарелым ААРБ представляют серьезную проблему для диагностики и лечения. При неэффективности консервативного лечения, необходимо перейти к деротационной halo-тракции с возможным использованием открытой коррекции и задней фиксации. Целью лечения является устранение кривошеи и болей за счет создания правильного соотношения С1-С2. Движения в атланто-аксиальном суставе не восстанавливаются из-за образования фиброзного или костного блока

Comparative study of density functional theories of the exchange-correlation hole and energy in silicon

We present a detailed study of the exchange-correlation hole and exchange-correlation energy per particle in the Si crystal as calculated by the Variational Monte Carlo method and predicted by various density functional models. Nonlocal density averaging methods prove to be successful in correcting severe errors in the local density approximation (LDA) at low densities where the density changes dramatically over the correlation length of the LDA hole, but fail to provide systematic improvements at higher densities where the effects of density inhomogeneity are more subtle. Exchange and correlation considered separately show a sensitivity to the nonlocal semiconductor crystal environment, particularly within the Si bond, which is not predicted by the nonlocal approaches based on density averaging. The exchange hole is well described by a bonding orbital picture, while the correlation hole has a significant component due to the polarization of the nearby bonds, which partially screens out the anisotropy in the exchange hole.Comment: 16 pages, 5 figures, RevTeX, added conten

Determination of the Deep Inelastic Contribution to the Generalised Gerasimov-Drell-Hearn Integral for the Proton and Neutron

The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2] for the proton and neutron have been determined from measurements of polarised cross section asymmetries in deep inelastic scattering of 27.5 GeV longitudinally polarised positrons from polarised 1H and 3He internal gas targets. The data were collected in the region above the nucleon resonances in the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the proton the contribution to the generalised Gerasimov-Drell-Hearn integral was found to be substantial and must be included for an accurate determination of the full integral. Furthermore the data are consistent with a QCD next-to-leading order fit based on previous deep inelastic scattering data. Therefore higher twist effects do not appear significant.Comment: 6 pages, 3 figures, 1 table, revte

Observation of a Coherence Length Effect in Exclusive Rho^0 Electroproduction

Exclusive incoherent electroproduction of the rho^0(770) meson from 1H, 2H, 3He, and 14N targets has been studied by the HERMES experiment at squared four-momentum transfer Q**2>0.4 GeV**2 and positron energy loss nu from 9 to 20 GeV. The ratio of the 14N to 1H cross sections per nucleon, known as the nuclear transparency, was found to decrease with increasing coherence length of quark-antiquark fluctuations of the virtual photon. The data provide clear evidence of the interaction of the quark- antiquark fluctuations with the nuclear medium.Comment: RevTeX, 5 pages, 3 figure

Measurement of the Neutron Spin Structure Function g1ng_1^n with a Polarized ^3He Target

Results are reported from the HERMES experiment at HERA on a measurement of the neutron spin structure function $g_1^n(x,Q^2)$ in deep inelastic scattering using 27.5 GeV longitudinally polarized positrons incident on a polarized $^3$He internal gas target. The data cover the kinematic range $0.023<x<0.6$ and $1 (GeV/c)^2 < Q^2 <15 (GeV/c)^2$. The integral $\int_{0.023}^{0.6} g_1^n(x) dx$ evaluated at a fixed $Q^2$ of $2.5 (GeV/c)^2$ is $-0.034\pm 0.013(stat.)\pm 0.005(syst.)$. Assuming Regge behavior at low $x$, the first moment $\Gamma_1^n=\int_0^1 g_1^n(x) dx$ is $-0.037\pm 0.013(stat.)\pm 0.005(syst.)\pm 0.006(extrapol.)$.Comment: 4 pages TEX, text available at http://www.krl.caltech.edu/preprints/OAP.htm

Flavor Decomposition of the Polarized Quark Distributions in the Nucleon from Inclusive and Semi-inclusive Deep-inelastic Scattering

Spin asymmetries of semi-inclusive cross sections for the production of positively and negatively charged hadrons have been measured in deep-inelastic scattering of polarized positrons on polarized hydrogen and 3He targets, in the kinematic range 0.023<x<0.6 and 1 GeV^2<Q^2<10 GeV^2. Polarized quark distributions are extracted as a function of x for up $(u+u_bar) and down (d+d_bar) flavors. The up quark polarization is positive and the down quark polarization is negative in the measured range. The polarization of the sea is compatible with zero. The first moments of the polarized quark distributions are presented. The isospin non-singlet combination Delta_q_3 is consistent with the prediction based on the Bjorken sum rule. The moments of the polarized quark distributions are compared to predictions based on SU(3)_f flavor symmetry and to a prediction from lattice QCD.Comment: 14 pages, 6 figures (eps format), 10 tables in Latex New version contains tables of asymmetries and correlation matri

Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the $\gamma p$ centre of mass energy is consistent with diffractive scattering. For total transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil

Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV

Results are presented from a search for a W' boson using a dataset corresponding to 5.0 inverse femtobarns of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV. The W' boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both left-handed and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W' to t b, leading to a final state signature with a single lepton (e, mu), missing transverse energy, and jets, at least one of which is tagged as a b-jet. A W' boson that couples to fermions with the same coupling constant as the W, but to the right-handed rather than left-handed chiral projections, is excluded for masses below 1.85 TeV at the 95% confidence level. For the first time using LHC data, constraints on the W' gauge coupling for a set of left- and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe