326 research outputs found
All-Optical Production of Chromium Bose-Einstein Condensates
We report on the production of ^52Cr Bose Einstein Condensates (BEC) with an
all-optical method. We first load 5.10^6 metastable chromium atoms in a 1D
far-off-resonance optical trap (FORT) from a Magneto Optical Trap (MOT), by
combining the use of Radio Frequency (RF) frequency sweeps and depumping
towards the ^5S_2 state. The atoms are then pumped to the absolute ground
state, and transferred into a crossed FORT in which they are evaporated. The
fast loading of the 1D FORT (35 ms 1/e time), and the use of relatively fast
evaporative ramps allow us to obtain in 20 s about 15000 atoms in an almost
pure condensate.Comment: 4 pages, 4 figure
potential biomarkers of haemophilic arthropathy correlations with compatible additive magnetic resonance imaging scores
Introduction: Although biomarkers are useful diagnostic tools to assess joint damage in osteoarthritis and rheumatoid arthritis, few data exist for biomarkers of haemophilic arthropathy. Aim: To evaluate the association between biomarkers and compatible additive magnetic resonance imaging (MRI) scores in patients with severe haemophilia A. Methods: Patients aged 12–35 years with no history of factor VIII (FVIII) inhibitors were enrolled in a controlled, cross-sectional, multinational investigation. Patients received primary or secondary prophylaxis or on-demand treatment with FVIII and underwent MRI on four joints (two ankles, two knees). Soluble biomarkers of cartilage and bone degradation, inflammation, and angiogenesis were assessed (serum levels of C-terminal telopeptides of type I collagen [CTX-I], cartilage oligomeric matrix protein [COMP], chondroitin-sulphate aggrecan turnover 846 epitope [CS846], tissue inhibitor of metalloproteinase 1 [TIMP-1]; plasma levels of vascular endothelial growth factor [VEGF], matrix metalloproteinases 3 and 9 [MMP3, MMP9]). Relationships between biomarkers and MRI scores were evaluated using Spearman rank correlation. Results: Biomarkers were assessed in 117 of 118 per-protocol patients. Mean and median CTX-I, COMP, TIMP-1, MMP3, MMP9, and VEGF values were within normal ranges (reference range not available for CS846 in healthy volunteers). No correlations between biomarkers and MRI scores were found, with the exception of CS846, which showed significant correlation in a subgroup of 22 on-demand patients (r = 0.436; P = 0.04). Conclusions: Compatible additive MRI scores showed no clear correlations with any of the potential biomarkers for haemophilic arthropathy in the overall population. CS846 levels were significantly correlated with MRI scores in patients treated on demand. (Less
Superfield covariant analysis of the divergence structure of noncommutative supersymmetric QED
Commutative supersymmetric Yang-Mills is known to be renormalizable for
, while finite for . However, in the
noncommutative version of the model (NCSQED) the UV/IR mechanism gives rise
to infrared divergences which may spoil the perturbative expansion. In this
work we pursue the study of the consistency of NCSQED by working
systematically within the covariant superfield formulation. In the Landau
gauge, it has already been shown for that the gauge field
two-point function is free of harmful UV/IR infrared singularities, in the
one-loop approximation. Here we show that this result holds without
restrictions on the number of allowed supersymmetries and for any arbitrary
covariant gauge. We also investigate the divergence structure of the gauge
field three-point function in the one-loop approximation. It is first proved
that the cancellation of the leading UV/IR infrared divergences is a gauge
invariant statement. Surprisingly, we have also found that there exist
subleading harmful UV/IR infrared singularities whose cancellation only takes
place in a particular covariant gauge. Thus, we conclude that these last
mentioned singularities are in the gauge sector and, therefore, do not
jeopardize the perturbative expansion and/or the renormalization of the theory.Comment: 36 pages, 11 figures. Minor correction
Radio-frequency induced ground state degeneracy in a Chromium Bose-Einstein condensate
We study the effect of strong radio-frequency (rf) fields on a chromium
Bose-Einstein condensate (BEC), in a regime where the rf frequency is much
larger than the Larmor frequency. We use the modification of the Land\'{e}
factor by the rf field to bring all Zeeman states to degeneracy, despite the
presence of a static magnetic field of up to 100 mG. This is demonstrated by
analyzing the trajectories of the atoms under the influence of dressed magnetic
potentials in the strong field regime. We investigate the problem of
adiabaticity of the rf dressing process, and relate it to how close the dressed
states are to degeneracy. Finally, we measure the lifetime of the rf dressed
BECs, and identify a new rf-assisted two-body loss process induced by
dipole-dipole interactions.Comment: 4 pages, 4 figure
Random Matrix Theory of Transition Strengths and Universal Magnetoconductance in the Strongly Localized Regime
Random matrix theory of the transition strengths is applied to transport in
the strongly localized regime. The crossover distribution function between the
different ensembles is derived and used to predict quantitatively the {\sl
universal} magnetoconductance curves in the absence and in the presence of
spin-orbit scattering. These predictions are confirmed numerically.Comment: 15 pages and two figures in postscript, revte
Theory of nonlinear sub-Doppler laser spectroscopy taking into account atomic-motion-induced density-dependent effects in a gas
We develop a field-nonlinear theory of sub-Doppler spectroscopy in a gas of
two-level atoms, based on a self-consistent solution of the Maxwell-Bloch
equations in the mean field and single-atom density matrix approximations. This
makes it possible to correctly take into account the effects caused by the free
motion of atoms in a gas, which lead to a nonlinear dependence of the
spectroscopic signal on the atomic density even in the absent of a direct
interatomic interaction (e.g., dipole-dipole interaction). Within the framework
of this approach, analytical expressions for the light field were obtained for
an arbitrary number of resonant waves and arbitrary optical thickness of a gas
medium. Sub-Doppler spectroscopy in the transmission signal for two
counterpropagating and co-propagating waves has been studied in detail. A
previously unknown red shift of a narrow sub-Doppler resonance is predicted in
a counterpropagating waves scheme, when the frequency of one wave is fixed and
the frequency of the other wave is varied. The magnitude of this shift depends
on the atomic density and can be more than an order of magnitude greater than
the known shift from the interatomic dipole-dipole interaction (Lorentz-Lorenz
shift). The found effects, caused by the free motion of atoms, require a
significant revision of the existing picture of spectroscopic effects depending
on the density of atoms in a gas. Apart of fundamental aspect, obtained results
are important for precision laser spectroscopy and optical atomic clocks.Comment: 18 pages, 12 figure
Exact results in planar N=1 superconformal Yang-Mills theory
In the \beta-deformed N=4 supersymmetric SU(N) Yang-Mills theory we study the
class of operators O_J = Tr(\Phi_i^J \Phi_k), i\neq k and compute their exact
anomalous dimensions for N,J\to\infty. This leads to a prediction for the
masses of the corresponding states in the dual string theory sector. We test
the exact formula perturbatively up to two loops. The consistency of the
perturbative calculation with the exact result indicates that in the planar
limit the one--loop condition g^2=h\bar{h} for superconformal invariance is
indeed sufficient to insure the {\em exact} superconformal invariance of the
theory. We present a direct proof of this point in perturbation theory. The O_J
sector of this theory shares many similarities with the BMN sector of the N=4
theory in the large R--charge limit.Comment: LaTex, 14 pages, 3 figures; v2: minor corrections and one reference
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High strength tubular columns and connections under earthquake, fire loading and fatigue
High strength steel (HSS) has been available for many years. However, its use in onshore engineeringis quite restrictive. Nonetheless very recently, there was a growing trend for the use of HSS in tubularstructures thanks to Eurocode 3 Part 1-12 (2006) that extended its scope to steel grades up toS690/S700MC. Nonetheless, Eurocode 3 Part 1-12 imposes many limitations at thematerial, structuraland design level. The ambitious targets of two EU funded –ATTEL and HITUBES – projects are toincrease the performance of tubular structures, reduce weights, construction and operating costs bychange in conceptual design and implementation of HSS. In a greater detail, the intent of the ATTELproject, is to promote the use of HSS members endowed with circular hollow sections in buildings subjectto earthquake and fire, in order to understand the actual behaviour of HSS material and to show the possiblebenefits with respect to mild steel. The buildings were realized with TS590 for steel columns and S275 forbeams in order to satisfy the capacity design criterion for columns and beams under earthquakeloading. The preliminary design of these structures leaned towards two fundamental conclusions: i) the costbenefits related to the use of HSS columns in braced frames, which are mainly subjected to axialloads and low bending moments; ii) the cost benefits related to the use of HHS columns in unbraced framesonly achieved along the main direction and for "medium" earthquake loading (<0.25g). Physical testsboth on full scale beam-to-column joints and column base joints to be performed at the University of Trentowill allow details for these important components to be checked. As far as the HITUBES project is concerned,the main work regards members and joints subject to monotonic, low-cycle and high-cycle fatigue loading.In particular, the project is focusing on: i) extraction of tubular welded and bolted joints from two casestudies, i.e. a footbridge and a railway bridge, respectively; ii) definition of weld condition –overmatching andundermatching – electrode selection and post-weld treatment –peening- for welded tubular joints
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