204 research outputs found
Anomalous Behavior of Spin Systems with Dipolar Interactions
We study the properties of spin systems realized by cold polar molecules
interacting via dipole-dipole interactions in two dimensions. Using a spin wave
theory, that allows for the full treatment of the characteristic long-distance
tail of the dipolar interaction, we find several anomalous features in the
ground state correlations and the spin wave excitation spectrum, which are
absent in their counterparts with short range interaction. The most striking
consequence is the existence of true long-range order at finite temperature for
a two-dimensional phase with a broken U(1) symmetry.Comment: 6 pages, 3 figure
Praxisforschungsnetzwerke - Eine explorative Studie mit Akteuren der ökologischen Landwirtschaft in Hessen
In der Praxisforschung werden LandwirtInnen als aktiv Handelnde in den Forschungsprozess eingebunden. LandwirtInnen, BeraterInnen und ForscherInnen gestalten Fragen und Inhalte gemeinsam. Dadurch entstehen Synergieeffekte, die Innovationen fĂŒr eine nachhaltige Landwirtschaft hervorbringen. Durch langjĂ€hrige Zusammenarbeit in Netzwerken kann erfolgsentscheidenes Vertrauen zwischen den Akteuren aufgebaut werden.
In der vorliegenden Untersuchung wurden im April 2018 acht Akteure aus Hessen (LandwirtInnen, BeraterInnen und ForscherInnen) zur Praxisforschung in Hessen befragt. Hierzu wurde die Methode der Fokusgruppendiskussion genutzt. Die befragten Akteure nehmen eine Expertenstellung innerhalb ihrer Akteursgruppe ein. Die Analyse der Fokusgruppendiskussion zeigt, dass zur Zeit nur wenig Praxisforschung in Hessen betrieben wird und die Akteursgruppen schlecht untereinander vernetzt sind. Die Rahmenbedingungen fĂŒr intensivere Zusammenarbeit sind sehr gut: Finanzmittel stehen zur VerfĂŒgung (Ăkoaktionsplan), es gibt motivierte Akteure, es sind viele UniversitĂ€ten ansĂ€ssig und erfolgreiche EIP-Projekte bieten eine gute Ausgangsbasis.
Um Praxisforschung im ökologischen Landbau in Hessen zu etablieren, werden AnsprechpartnerInnen und eine entsprechende Institutionalisierung benötigt. Die VĂL (Vereinigung Ăkologischer Landbau in Hessen e.V.) bietet interessante Voraussetzungen fĂŒr die Koordination eines Praxisforschungsnetzwerks. Die zur Zeit limitierte Versuchstechnik, eingeschrĂ€nkte zeitliche KapazitĂ€ten und rĂ€umliche Distanzen mĂŒssen dabei ebenso realistisch berĂŒcksichtigt werden wie eine faire Kostenverteilung
Coupling a single electron to a Bose-Einstein condensate
The coupling of electrons to matter is at the heart of our understanding of
material properties such as electrical conductivity. One of the most intriguing
effects is that electron-phonon coupling can lead to the formation of a Cooper
pair out of two repelling electrons, the basis for BCS superconductivity. Here
we study the interaction of a single localized electron with a Bose-Einstein
condensate (BEC) and show that it can excite phonons and eventually set the
whole condensate into a collective oscillation. We find that the coupling is
surprisingly strong as compared to ionic impurities due to the more favorable
mass ratio. The electron is held in place by a single charged ionic core
forming a Rydberg bound state. This Rydberg electron is described by a
wavefunction extending to a size comparable to the dimensions of the BEC,
namely up to 8 micrometers. In such a state, corresponding to a principal
quantum number of n=202, the Rydberg electron is interacting with several tens
of thousands of condensed atoms contained within its orbit. We observe
surprisingly long lifetimes and finite size effects due to the electron
exploring the wings of the BEC. Based on our results we anticipate future
experiments on electron wavefunction imaging, investigation of phonon mediated
coupling of single electrons, and applications in quantum optics.Comment: 4 pages, 3 figures and supplementary informatio
Pseudoscalar meson photoproduction: from known to undiscovered resonances
The role of dynamics in spin observables for pseudoscalar meson
photoproduction is investigated using a density matrix approach in a multipole
truncated framework. Extraction of novel rules for and reactions based on resonance dominance, and on
other broad and reasonable dynamical assumptions, are discussed. Observables
that are particularly sensitive to missing nucleonic resonances predicted by
quark-based approaches, are singled out.Comment: 22 pages, latex, 3 figure
Recommended from our members
Topological bands with a Chern number C = 2 by dipolar exchange interactions
We demonstrate the realization of topological band structures by exploiting the intrinsic spin-orbit coupling of dipolar interactions in combination with broken time-reversal symmetry. The system is based on polar molecules trapped in a deep optical lattice, where the dynamics of rotational excitations follows a hopping Hamiltonian which is determined by the dipolar exchange interactions. We find topological bands with Chern number C=2 on the square lattice, while a very rich structure of different topological bands appears on the honeycomb lattice. We show that the system is robust against missing molecules. For certain parameters we obtain flat bands, providing a promising candidate for the realization of hard-core bosonic fractional Chern insulators.Physic
Comparison of adjuvant gemcitabine and capecitabine with gemcitabine monotherapy in patients with resected pancreatic cancer (ESPAC-4): a multicentre, open-label, randomised, phase 3 trial
BACKGROUND: The ESPAC-3 trial showed that adjuvant gemcitabine is the standard of care based on similar survival to and less toxicity than adjuvant 5-fluorouracil/folinic acid in patients with resected pancreatic cancer. Other clinical trials have shown better survival and tumour response with gemcitabine and capecitabine than with gemcitabine alone in advanced or metastatic pancreatic cancer. We aimed to determine the efficacy and safety of gemcitabine and capecitabine compared with gemcitabine monotherapy for resected pancreatic cancer. METHODS: We did a phase 3, two-group, open-label, multicentre, randomised clinical trial at 92 hospitals in England, Scotland, Wales, Germany, France, and Sweden. Eligible patients were aged 18 years or older and had undergone complete macroscopic resection for ductal adenocarcinoma of the pancreas (R0 or R1 resection). We randomly assigned patients (1:1) within 12 weeks of surgery to receive six cycles of either 1000 mg/m(2) gemcitabine alone administered once a week for three of every 4 weeks (one cycle) or with 1660 mg/m(2) oral capecitabine administered for 21 days followed by 7 days' rest (one cycle). Randomisation was based on a minimisation routine, and country was used as a stratification factor. The primary endpoint was overall survival, measured as the time from randomisation until death from any cause, and assessed in the intention-to-treat population. Toxicity was analysed in all patients who received trial treatment. This trial was registered with the EudraCT, number 2007-004299-38, and ISRCTN, number ISRCTN96397434. FINDINGS: Of 732 patients enrolled, 730 were included in the final analysis. Of these, 366 were randomly assigned to receive gemcitabine and 364 to gemcitabine plus capecitabine. The Independent Data and Safety Monitoring Committee requested reporting of the results after there were 458 (95%) of a target of 480 deaths. The median overall survival for patients in the gemcitabine plus capecitabine group was 28·0 months (95% CI 23·5-31·5) compared with 25·5 months (22·7-27·9) in the gemcitabine group (hazard ratio 0·82 [95% CI 0·68-0·98], p=0·032). 608 grade 3-4 adverse events were reported by 226 of 359 patients in the gemcitabine plus capecitabine group compared with 481 grade 3-4 adverse events in 196 of 366 patients in the gemcitabine group. INTERPRETATION: The adjuvant combination of gemcitabine and capecitabine should be the new standard of care following resection for pancreatic ductal adenocarcinoma
Opposite-side flavour tagging of B mesons at the LHCb experiment
The calibration and performance of the oppositeside
flavour tagging algorithms used for the measurements
of time-dependent asymmetries at the LHCb experiment
are described. The algorithms have been developed using
simulated events and optimized and calibrated with
B
+ âJ/ÏK
+, B0 âJ/ÏK
â0 and B0 âD
ââ
Ό
+
ΜΌ decay
modes with 0.37 fbâ1 of data collected in pp collisions
at
â
s = 7 TeV during the 2011 physics run. The oppositeside
tagging power is determined in the B
+ â J/ÏK
+
channel to be (2.10 ± 0.08 ± 0.24) %, where the first uncertainty
is statistical and the second is systematic
- âŠ