Impurity Energy Level Within The Haldane Gap

An impurity bond $J{'}$ in a periodic 1D antiferromagnetic, spin 1 chain with exchange $J$ is considered. Using the numerical density matrix renormalization group method, we find an impurity energy level in the Haldane gap, corresponding to a bound state near the impurity bond. When $J{'}<J$ the level changes gradually from the edge of the Haldane gap to the ground state energy as the deviation $dev=(J-J{'})/J$ changes from 0 to 1. It seems that there is no threshold. Yet, there is a threshold when $J{'}>J$. The impurity level appears only when the deviation $dev=(J{'}-J)/J{'}$ is greater than $B_{c}$, which is near 0.3 in our calculation.Comment: Latex file,9 pages uuencoded compressed postscript including 4 figure

CuSiO_3 : a quasi - one - dimensional S=1/2 antiferromagnetic chain system

CuSiO_3, isotypic to the spin - Peierls compound CuGeO_3, was discovered recently as a metastable decomposition product of the silicate mineral dioptase, Cu_6Si_6O_{18}\cdot6H_2O. We investigated the physical properties of CuSiO_3 using susceptibility, magnetization and specific heat measurements on powder samples. The magnetic susceptibility \chi(T) is reproduced very well above T = 8 K by theoretical calculations for an S=1/2 antiferromagnetic Heisenberg linear chain without frustration (\alpha = 0) and a nearest - neighbor exchange coupling constant of J/k_{B} = 21 K, much weaker than in CuGeO_3. Below 8 K the susceptibility exhibits a substantial drop. This feature is identified as a second - order phase transition at T_{0} = 7.9 K by specific heat measurements. The influence of magnetic fields on T_{0} is weak, and ac - magnetization measurements give strong evidence for a spin - flop - phase at \mu_0H_{SF} ~ 3 T. The origin of the magnetic phase transition at T_{0} = 7.9 K is discussed in the context of long - range antiferromagnetic order (AF) versus spin - Peierls(SP)order. Susceptibility and specific heat results support the AF ordered ground state. Additional temperature dependent ^{63,65}Cu nuclear quadrupole resonance experiments have been carried out to probe the Cu^{2+} electronic state and the spin dynamics in CuSiO_3

Finite Temperature Properties of Quantum Antiferromagnets in a Uniform Magnetic Field in One and Two Dimensions

Consider a $d$-dimensional antiferromagnet with a quantum disordered ground state and a gap to bosonic excitations with non-zero spin. In a finite external magnetic field, this antiferromagnet will undergo a phase transition to a ground state with non-zero magnetization, describable as the condensation of a dilute gas of bosons. The finite temperature properties of the Bose gas in the vicinity of this transition are argued to obey a hypothesis of ZERO SCALE-FACTOR UNIVERSALITY for $d < 2$, with logarithmic violations in $d=2$. Scaling properties of various experimental observables are computed in an expansion in $\epsilon=2-d$, and exactly in $d=1$.Comment: 27 pages, REVTEX 3.0, 8 Postscript figures appended, YCTP-xyz

Haldane-Gapped Spin Chains as Luttinger Liquids: Correlation Functions at Finite Field

We study the behavior of Heisenberg, antiferromagnetic, integer-spin chains in the presence of a magnetic field exceeding the attendant spin gap. For temperatures much smaller than the gap, the spin chains exhibit Luttinger liquid behavior. We compute exactly both the corresponding Luttinger parameter and the Fermi velocity as a function of magnetic field. This enables the computation of a number of correlators from which we derive the spin conductance, the expected form of the dynamic structure factor relevant to inelastic neutron scattering experiments, and NMR relaxation rates. We also comment upon the robustness of the magnetically induced gapless phase both to finite temperature and finite couplings between neighbouring chains.Comment: 32 pages, 8 figures; published version includes additions discussing the robustness of the magnetically induced gapless phase to ordering between chains as well as the relationship between the spin-1 chains and spin-1/2 ladders in the presence of a magnetic fiel

Measurement of gamma gamma -> p p-bar production at Belle

A high precision study of the process gamma gamma -> p p-bar has been performed using a data sample of 89/fb collected with the Belle detector at the KEKB e+e- collider. The cross section of p p-bar production has been measured at two-photon center-of-mass (c.m.) energies between 2.025 and 4.0 GeV and in the c.m. angular range of |cos(theta^*)| eta_c -> p p-bar is observed and the product of the two-photon width of the eta_c and its branching ratio to p p-bar is determined.Comment: 20 pages, 9 figures, Fig.1 added, accepted for publication in Phys. Lett.

Functional outcomes in symptomatic versus asymptomatic patients undergoing incisional hernia repair: Replacing one problem with another? A prospective cohort study in 1312 patients

Background: Incisional hernias can be associated with pain or discomfort. Surgical repair especially mesh reinforcement, may likewise induce pain. The primary objective was to assess the incidence of pain after hernia repair in patients with and without pre-operative pain or discomfort. The secondary objectives were to determine the preferred mesh type, mesh location and surgical technique in minimizing postoperative pain or discomfort. Materials and methods: A registry-based prospective cohort study was performed, including patients undergoing incisional hernia repair between September 2011 and May 2019. Patients with a minimum follow-up of 3–6 months were included. The incidence of hernia related pain and discomfort was recorded perioperatively. Results: A total of 1312 patients were included. Pre-operatively, 1091 (83%) patients reported pain or discomfort. After hernia repair, 961 (73%) patients did not report pain or discomfort (mean follow-up = 11.1 months). Of the pre-operative asymptomatic patients (n = 221), 44 (20%, moderate or severe pain: n = 14, 32%) reported pain or discomfort after mean follow-up of 10.5 months. Of those patients initially reporting pain or discomfort (n = 1091), 307 (28%, moderate or severe pain: n = 80, 26%) still reported pain or discomfort after a mean follow-up of 11.3 months postoperatively. Conclusion: In symptomatic incisional hernia patients, hernia related complaints may be resolved in the majority of cases undergoing surgical repair. In asymptomatic incisional hernia patients, pain or discomfort may be induced in a considerable number of patients due to surgical repair and one should be aware if this postoperative complication

The inner dust coma of Comet 26P Grigg-Skjellerup: multiple jets and nucleus fragments?

On 1992 July 10 the European Space Agency's spaceprobe Giotto passed the nucleus of the comparatively inactive comet 26P/Grigg-Skjellerup at a relative velocity of 14 km s(-1). This Giotto Extended Mission (GEM) followed a highly successful encounter in 1986 with Comet 1P/Halley. We present results returned from the Optical Probe Experiment (OPE) and in particular consider data gathered by the channels sensitive to the scattering of solar light by cometary dust grains, in emission-free continuum bands. Owing to the demise of the Halley Multicolour Camera (HMC) during the Halley encounter, and the low number of impacts registered by the Dust Impact Detection System (DIDSY), OPE data offer the best indication of the actual encounter geometry. We find that it is likely that Giotto was on the sunward side of the shadow terminator plane at closest approach, with our modelling results suggesting that Giotto passed similar to 100 km from the nucleus (although distances of up to 300 km cannot be ruled out). We investigate possible causes of the striking 'spike' features, or 'events', in the OPE data. While scattering of sunlight from ejecta particles as a result of dust impacts on the spacecraft body cannot be ruled out, considerations of the hypervelocity impact mechanisms and impact geometry show that this explanation is not without problems, and more investigation is needed before it can be conclusively accepted. As an alternative solution, we find that the complex data profiles can be fitted by jet activity in the innermost coma (which was not resolvable by ground-based observers). One particular event occurring at least 1000 km from the nucleus can be fitted if the OPE line of sight passes close to a nucleus fragment of radius 10-100 m which is situated around 50 km from the spacecraft and which is producing a small dust coma

Corrélation β-polarisation circulaire γ. Éléments de matrice nucléaires des transitions β. Cas du 86Rb

In order to determine the nuclear matrix elements (N.M.E.) for the β transition 86Rb (2- ; g.s.) → 86Sr (2 + ; 1.08 MeV), we measured the circular polarization of the 1.08 MeV γ in coincidence with the β spectrum for a few values of the angle θ βγ. The results are not in agreement with previous experiments. Our data and those from β-γ directional correlation and β spectrum shape factor were used to derive the six N.M.E. by fitting the experimental data with Morita and Morita's theoretical expressions. The N.M.E. obtained are compared with Walhborn's theoretical predictions. Some of his conclusions might have to be modified.En vue de la détermination des éléments de matrice nucléaires (E.M.N.) de la transition β 86Rb (2-) → 86Sr (2 + ; 1, 08 MeV), on a mesuré la polarisation circulaire du γ de 1,08 MeV, en coïncidence avec le spectre β, pour différentes valeurs de l'angle θβγ. Les résultats obtenus ne sont pas en accord avec des mesures antérieures. Ces résultats expérimentaux, ainsi que ceux relatifs à la corrélation directionnelle β-γ et au facteur de forme du spectre β, ont été utilisés pour déterminer les six E.M.N., par ajustement des expressions théoriques de Morita et Morita aux données expérimentales. Les valeurs obtenues pour les E.M.N. sont comparées aux prédictions théoriques de S. Walhborn. Certaines conclusions de Walhborn pourraient être modifiées