1,090 research outputs found
Phase diagram of the one-dimensional extended attractive Hubbard model for large nearest-neighbor repulsion
We consider the extended Hubbard model with attractive on-site interaction U
and nearest-neighbor repulsions V. We construct an effective Hamiltonian
H_{eff} for hopping t<<V and arbitrary U<0. Retaining the most important terms,
H_{eff} can be mapped onto two XXZ models, solved by the Bethe ansatz. The
quantum phase diagram shows two Luttinger liquid phases and a region of phase
separation between them. For density n<0.422 and U<-4, singlet superconducting
correlations dominate at large distances. For some parameters, the results are
in qualitative agreement with experiments in BaKBiO.Comment: 6 pages, 3 figures, submitted to Phys. Rev.
Far-infrared study of the Jahn-Teller distorted C60 monoanion in C60 tetraphenylphosphoniumiodide
We report high-resolution far-infrared transmission measurements on C(60)-tetraphenylphosphoniumiodide as a function of temperature. In the spectral region investigated (20-650 cm(-1)), we assign intramolecular modes of the C(60) monoanion and identify low-frequency combination modes. The well-known F(1u)(1) and F(1u)(2) modes are split into doublers at room temperature, indicating a D(5d) or D(3d) distorted ball. This result is consistent with a dynamic Jahn-Teller effect in the strong-coupling limit or with a static distortion stabilized by low-symmetry perturbations. The appearance of silent odd modes is in keeping with symmetry reduction of the hall, while activation of even modes is attributed to interband electron-phonon coupling and orientational disorder in the fulleride salt. Temperature dependences reveal a weak transition in the region 125-150 K in both C(60)(-) and counterion modes, indicating a bulk, rather than solely molecular, effect. Anomalous softening (with decreasing temperature) in several modes may correlate with the radial character of those vibrations. [S0163-1829(98)03245-7]
Ancient Migratory Events in the Middle East: New Clues from the Y-Chromosome Variation of Modern Iranians
Knowledge of high resolution Y-chromosome haplogroup diversification within Iran provides important geographic context regarding the spread and compartmentalization of male lineages in the Middle East and southwestern Asia. At present, the Iranian population is characterized by an extraordinary mix of different ethnic groups speaking a variety of Indo-Iranian, Semitic and Turkic languages. Despite these features, only few studies have investigated the multiethnic components of the Iranian gene pool. In this survey 938 Iranian male DNAs belonging to 15 ethnic groups from 14 Iranian provinces were analyzed for 84 Y-chromosome biallelic markers and 10 STRs. The results show an autochthonous but non-homogeneous ancient background mainly composed by J2a sub-clades with different external contributions. The phylogeography of the main haplogroups allowed identifying post-glacial and Neolithic expansions toward western Eurasia but also recent movements towards the Iranian region from western Eurasia (R1b-L23), Central Asia (Q-M25), Asia Minor (J2a-M92) and southern Mesopotamia (J1-Page08). In spite of the presence of important geographic barriers (Zagros and Alborz mountain ranges, and the Dasht-e Kavir and Dash-e Lut deserts) which may have limited gene flow, AMOVA analysis revealed that language, in addition to geography, has played an important role in shaping the nowadays Iranian gene pool. Overall, this study provides a portrait of the Y-chromosomal variation in Iran, useful for depicting a more comprehensive history of the peoples of this area as well as for reconstructing ancient migration routes. In addition, our results evidence the important role of the Iranian plateau as source and recipient of gene flow between culturally and genetically distinct population
How do patients with inflammatory bowel disease want their biological therapy administered?
<p>Abstract</p> <p>Background</p> <p>Infliximab is usually administered by two monthly intravenous (iv) infusions, therefore requiring visits to hospital. Adalimumab is administered by self subcutaneous (sc) injections every other week. Both of these anti-TNF drugs appear to be equally efficacious in the treatment of Crohn's Disease and therefore the decision regarding which drug to choose will depend to some extent on patient choice, which may be based on the mode of administration.</p> <p>The aims of this study were to compare preferences in Inflammatory Bowel Disease (IBD) patients for two currently available anti-TNF agents and the reasons for their choices.</p> <p>Methods</p> <p>An anonymous questionnaire was distributed to IBD patients who had attended the Gastroenterology service (Ulster Hospital, Dundonald, Belfast, N. Ireland. UK) between January 2007 and December 2007. The patients were asked in a hypothetical situation if the following administering methods of anti-TNF drugs (intravenous or subcutaneous) were available, which drug route of administration would they choose.</p> <p>Results</p> <p>One hundred and twenty-five patients fulfilled the inclusion criteria and were issued questionnaires, of these 78 questionnaires were returned (62 percent response). The mean age of respondent was 44 years. Of the total number of respondents, 33 patients (42 percent) preferred infliximab and 19 patients (24 percent) preferred adalimumab (p = 0.07). Twenty-six patients (33 percent) did not indicate a preference for either biological therapy and were not included in the final analysis. The commonest reason cited for those who chose infliximab (iv) was: <it>"I do not like the idea of self-injecting," </it>(67 percent). For those patients who preferred adalimumab (sc) the commonest reason cited was: <it>"I prefer the convenience of injecting at home," </it>(79 percent). Of those patients who had previously been treated with an anti-TNF therapy (n = 10, all infliximab) six patients stated that they would prefer infliximab if given the choice in the future (p = 0.75).</p> <p>Conclusions</p> <p>There was a trend towards patient preference for infliximab (iv) treatment as opposed to adalimumab (sc) in patients with IBD. This difference may be due to the frequency of administration, mode of administration or differing 'times in the market-place', as infliximab had been approved for a longer period of time in Crohn's disease. Further studies are required in IBD patients to investigate whether patient choice will affect compliance, patient satisfaction and efficacy of treatment with anti-TNF therapies.</p
Differential branching fraction and angular analysis of the decay B0→K∗0μ+μ−
The angular distribution and differential branching fraction of the decay B 0→ K ∗0 μ + μ − are studied using a data sample, collected by the LHCb experiment in pp collisions at s√=7 TeV, corresponding to an integrated luminosity of 1.0 fb−1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
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
+ →J/ψK
+, B0 →J/ψK
∗0 and B0 →D
∗−
μ
+
νμ decay
modes with 0.37 fb−1 of data collected in pp collisions
at
√
s = 7 TeV during the 2011 physics run. The oppositeside
tagging power is determined in the B
+ → J/ψK
+
channel to be (2.10 ± 0.08 ± 0.24) %, where the first uncertainty
is statistical and the second is systematic
Observation of two new baryon resonances
Two structures are observed close to the kinematic threshold in the mass spectrum in a sample of proton-proton collision data, corresponding
to an integrated luminosity of 3.0 fb recorded by the LHCb experiment.
In the quark model, two baryonic resonances with quark content are
expected in this mass region: the spin-parity and
states, denoted and .
Interpreting the structures as these resonances, we measure the mass
differences and the width of the heavier state to be
MeV,
MeV,
MeV, where the first and second
uncertainties are statistical and systematic, respectively. The width of the
lighter state is consistent with zero, and we place an upper limit of
MeV at 95% confidence level. Relative
production rates of these states are also reported.Comment: 17 pages, 2 figure
Measurement of the CP-violating phase phi_s in the decay Bs->J/psi phi
We present a measurement of the time-dependent CP-violating asymmetry in B_s
-> J/psi phi decays, using data collected with the LHCb detector at the LHC.
The decay time distribution of B_s -> J/psi phi is characterized by the decay
widths Gamma_H and Gamma_L of the heavy and light mass eigenstates of the
B_s-B_s-bar system and by a CP-violating phase phi_s. In a sample of about 8500
B_s -> J/psi phi events isolated from 0.37 fb^-1 of pp collisions at sqrt(s)=7
TeV we measure phi_s = 0.15 +/- 0.18 (stat) +/- 0.06 (syst) rad. We also find
an average B_s decay width Gamma_s == (Gamma_L + Gamma_H)/2 = 0.657 +/- 0.009
(stat) +/- 0.008 (syst) ps^-1 and a decay width difference Delta Gamma_s ==
Gamma_L - Gamma_H} = 0.123 +/- 0.029 (stat) +/- 0.011 (syst) ps^-1. Our
measurement is insensitive to the transformation (phi_s,DeltaGamma_s --> pi -
phi_s, - Delta Gamma_s.Comment: 9 pages, 3 figure
Measurements of the branching fractions of the decays B°s → D∓s K± and B°s → D¯sπ+
The decay mode B°s → D∓s K± allows for one of the theoretically cleanest measurements of the CKM angle γ through the study of time-dependent CP violation. This paper reports a measurement of its branching fraction relative to the Cabibbo-favoured mode B°s → D¯sπ+ based on a data sample corresponding to 0.37 fb¯¹ of proton-proton collisions at √s = 7TeV collected in 2011 with the LHCb detector. In addition, the ratio of B meson production fractions fs/fd, determined from semileptonic decays, together with the known branching fraction of the control channel B°s → D¯sπ+ is used to perform an absolute measurement of the branching fractions: B(B°s → D¯sπ+) = (2.95 ± 0.05 ± 0.17 -0.22 +0.18) × 10¯³ ; B(B°s → D∓s K±) = (1.90 ± 0.12 ± 0.13 -0.14 +0.12) × 10¯4 ; where the first uncertainty is statistical, the second the experimental systematic uncertainty, and the third the uncertainty due to f s/f
Search for CP violation in decays
A model-independent search for direct CP violation in the Cabibbo suppressed
decay in a sample of approximately 370,000 decays is
carried out. The data were collected by the LHCb experiment in 2010 and
correspond to an integrated luminosity of 35 pb. The normalized Dalitz
plot distributions for and are compared using four different
binning schemes that are sensitive to different manifestations of CP violation.
No evidence for CP asymmetry is found.Comment: 13 pages, 8 figures, submitted to Phys. Rev.
- …