Quantum Statistical Calculations and Symplectic Corrector Algorithms

The quantum partition function at finite temperature requires computing the trace of the imaginary time propagator. For numerical and Monte Carlo calculations, the propagator is usually split into its kinetic and potential parts. A higher order splitting will result in a higher order convergent algorithm. At imaginary time, the kinetic energy propagator is usually the diffusion Greens function. Since diffusion cannot be simulated backward in time, the splitting must maintain the positivity of all intermediate time steps. However, since the trace is invariant under similarity transformations of the propagator, one can use this freedom to "correct" the split propagator to higher order. This use of similarity transforms classically give rises to symplectic corrector algorithms. The split propagator is the symplectic kernel and the similarity transformation is the corrector. This work proves a generalization of the Sheng-Suzuki theorem: no positive time step propagators with only kinetic and potential operators can be corrected beyond second order. Second order forward propagators can have fourth order traces only with the inclusion of an additional commutator. We give detailed derivations of four forward correctable second order propagators and their minimal correctors.Comment: 9 pages, no figure, corrected typos, mostly missing right bracket

Genome-wide analysis of barrett's adenocarcinoma. a first step towards identifying patients at risk and developing therapeutic paths

BACKGROUND: Barrett's esophagus metaplasia is the key precursor lesion of esophageal adenocarcinoma. The aim of this study was to find a subset of markers that may allow the identification of patients at risk for esophageal adenocarcinoma, and to determine genes differentially expressed in esophageal squamous cell carcinoma. METHODS:Laser capture microdissection technique was applied to procure cells from defined regions. Genome-wide RNA profiling was performed on esophageal adenocarcinoma (n = 21), Barrett's esophagus (n = 20), esophageal squamous carcinoma (n = 9) and healthy esophageal biopsies (n = 18) using the Affymetrix Human Genome U133plus 2.0 array. Microarray results were validated by quantitative real-time polymerase chain reaction in a second and independent cohort and by immunohistochemistry of two putative markers in a third independent cohort. RESULTS:Through unsupervised hierarchical clustering and principal component analysis, samples were separated into four distinct groups that match perfectly with histology. Many genes down-regulated in esophageal cancers belong to the epidermal differentiation complex or the related GO-group "cornified envelope" of terminally differentiated keratinocytes. Similarly, retinol metabolism was strongly down-regulated. Genes showing strong overexpression in esophageal carcinomas belong to the GO groups extracellular region /matrix such as MMP1, CTHRC1, and INHBA. According to an analysis of genes strongly up-regulated in both esophageal adenocarcinoma and Barrett's esophagus, REG4 might be of particular interest as an early marker for esophageal adenocarcinoma. CONCLUSIONS:Our study provides high quality data, which could serve for identification of potential biomarkers of Barrett's esophagus at risk of esophageal adenocarcinoma progression

Progressive ataxia with oculo-palatal tremor and optic atrophy

The final publication is available at Springer via doi: 10.​1007/​s00415-013-7136-

Finite-Wavevector Electromagnetic Response of Fractional Quantized Hall States

A fractional quantized Hall state with filling fraction $\nu = p/(2mp+1)$ can be modeled as an integer quantized Hall state of transformed fermions, interacting with a Chern-Simons field. The electromagnetic response function for these states at arbitrary frequency and wavevector can be calculated using a semiclassical approximation or the Random Phase Approximation (RPA). However, such calculations do not properly take into account the large effective mass renormalization which is present in the Chern-Simons theory. We show how the mass renormalization can be incorporated in a calculation of the response function within a Landau Fermi liquid theory approach such that Kohn's theorem and the $f$-sum rules are properly satisfied. We present results of such calculations.Comment: 19 pages (REVTeX 3.0), 5 figures available on request; HU-CMT-93S0

Generalised Chern-Simons Theory of Composite Fermions in Bilayer Hall Systems

We present a field theory of Jain's composite fermion model as generalised to the bilayer quantum Hall systems. We define operators which create composite fermions and write the Hamiltonian exactly in terms of these operators. This is seen to be a complexified version of the familiar Chern Simons theory. In the mean-field approximation, the composite fermions feel a modified effective magnetic field exactly as happens in usual Chern Simons theories, and plateaus are predicted at the same values of filling factors as Lopez and Fradkin and Halperin . But unlike normal Chern Simons theories, we obtain all features of the first-quantised wavefunctions including its phase, modulus and correct gaussian factors at the mean field level. The familiar Jain relations for monolayers and the Halperin wavefunction for bilayers come out as special cases.Comment: Revtex file; 20 pages after processing; no figure

Electromagnetic characteristics and effective gauge theory of double-layer quantum Hall systems

The electromagnetic characteristics of double-layer quantum Hall systems are studied, with projection to the lowest Landau level taken into account and intra-Landau-level collective excitations treated in the single-mode approximation. It is pointed out that dipole-active excitations, both elementary and collective, govern the long-wavelength features of quantum Hall systems. In particular, the presence of the dipole-active interlayer out-of-phase collective excitations, inherent to double-layer systems, modifies the leading O(k) and O(k^{2}) long-wavelength characteristics (i.e., the transport properties and characteristic scale) of the double-layer quantum Hall states substantially. We apply bosonization techniques and construct from such electromagnetic characteristics an effective theory, which consists of three vector fields representing the three dipole-active modes, one interlayer collective mode and two inter-Landau-level cyclotron modes. This effective theory properly incorporates the spectrum of collective excitations on the right scale of the Coulomb energy and, in addition, accommodates the favorable transport properties of the standard Chern-Simons theories.Comment: 10 pages, Revtex, sec. II slightly shortened, to appear in Phys. Rev.

The SAMI Galaxy Survey: Asymmetry in Gas Kinematics and its links to Stellar Mass and Star Formation

We study the properties of kinematically disturbed galaxies in the SAMI Galaxy Survey using a quantitative criterion, based on kinemetry (Krajnovic et al.). The approach, similar to the application of kinemetry by Shapiro et al. uses ionised gas kinematics, probed by H{\alpha} emission. By this method 23+/-7% of our 360-galaxy sub-sample of the SAMI Galaxy Survey are kinematically asymmetric. Visual classifications agree with our kinemetric results for 90% of asymmetric and 95% of normal galaxies. We find stellar mass and kinematic asymmetry are inversely correlated and that kinematic asymmetry is both more frequent and stronger in low-mass galaxies. This builds on previous studies that found high fractions of kinematic asymmetry in low mass galaxies using a variety of different methods. Concentration of star forma- tion and kinematic disturbance are found to be correlated, confirming results found in previous work. This effect is stronger for high mass galaxies (log(M*) > 10) and indicates that kinematic disturbance is linked to centrally concentrated star formation. Comparison of the inner (within 0.5Re) and outer H{\alpha} equivalent widths of asymmetric and normal galaxies shows a small but significant increase in inner equivalent width for asymmetric galaxies.Comment: 29 pages, 21 figure

The Chandra X-ray Survey of Planetary Nebulae (ChanPlaNS): Probing Binarity, Magnetic Fields, and Wind Collisions

We present an overview of the initial results from the Chandra Planetary Nebula Survey (ChanPlaNS), the first systematic (volume-limited) Chandra X-ray Observatory survey of planetary nebulae (PNe) in the solar neighborhood. The first phase of ChanPlaNS targeted 21 mostly high-excitation PNe within ~1.5 kpc of Earth, yielding 4 detections of diffuse X-ray emission and 9 detections of X-ray-luminous point sources at the central stars (CSPNe) of these objects. Combining these results with those obtained from Chandra archival data for all (14) other PNe within ~1.5 kpc that have been observed to date, we find an overall X-ray detection rate of ~70%. Roughly 50% of the PNe observed by Chandra harbor X-ray-luminous CSPNe, while soft, diffuse X-ray emission tracing shocks formed by energetic wind collisions is detected in ~30%; five objects display both diffuse and point-like emission components. The presence of X-ray sources appears correlated with PN density structure, in that molecule-poor, elliptical nebulae are more likely to display X-ray emission (either point-like or diffuse) than molecule-rich, bipolar or Ring-like nebulae. All but one of the X-ray point sources detected at CSPNe display X-ray spectra that are harder than expected from hot (~100 kK) central star photospheres, possibly indicating a high frequency of binary companions to CSPNe. Other potential explanations include self-shocking winds or PN mass fallback. Most PNe detected as diffuse X-ray sources are elliptical nebulae that display a nested shell/halo structure and bright ansae; the diffuse X-ray emission regions are confined within inner, sharp-rimmed shells. All sample PNe that display diffuse X-ray emission have inner shell dynamical ages <~5x10^3 yr, placing firm constraints on the timescale for strong shocks due to wind interactions in PNe.Comment: 41 pages, 6 figures; submitted to the Astronomical Journa

Signals of Bose Einstein condensation and Fermi quenching in the decay of hot nuclear systems

We report experimental signals of Bose-Einstein condensation in the decay of hot Ca projectile-like sources produced in mid-peripheral collisions at sub-Fermi energies. The experimental setup, constituted by the coupling of the INDRA 4$\pi$ detector array to the forward angle VAMOS magnetic spectrometer, allowed us to reconstruct the mass, charge and excitation energy of the decaying hot projectile-like sources. Furthermore, by means of quantum fluctuation analysis techniques, temperatures and mean volumes per particle "as seen by" bosons and fermions separately are correlated to the excitation energy of the reconstructed system. The obtained results are consistent with the production of dilute mixed (bosons/fermions) systems, where bosons experience a smaller volume as compared to the surrounding fermionic gas. Our findings recall similar phenomena observed in the study of boson condensates in atomic traps.Comment: Submitted to Phys. Rev. Lett. (december 2014

New Herbig-Haro Objects and Giant Outflows in Orion

We present the results of a photographic and CCD imaging survey for Herbig-Haro (HH) objects in the L1630 and L1641 giant molecular clouds in Orion. The new HH flows were initially identified from a deep H-alpha film from the recently commissioned AAO/UKST H-alpha Survey of the southern sky. Our scanned H-alpha and broad band R images highlight both the improved resolution of the H-alpha survey and the excellent contrast of the H-alpha flux with respect to the broad band R. Comparative IVN survey images allow us to distinguish between emission and reflection nebulosity. Our CCD H-alpha, [SII], continuum and I band images confirm the presence of a parsec-scale HH flow associated with the Ori I-2 cometary globule and several parsec-scale strings of HH emission centred on the L1641-N infrared cluster. Several smaller outflows display one-sided jets. Our results indicate that for declinations south of -6 degrees in L1641, parsec-scale flows appear to be the major force in the large-scale movement of optical dust and molecular gas.Comment: 14 pages, Latex using MN style, 21 figures in JPEG format. Higher resolution figures available from S.L. Mader. Accepted by MNRAS. Email contact for higher resolution images: [email protected]