115 research outputs found
Fractal Strings and Multifractal Zeta Functions
For a Borel measure on the unit interval and a sequence of scales that tend
to zero, we define a one-parameter family of zeta functions called multifractal
zeta functions. These functions are a first attempt to associate a zeta
function to certain multifractal measures. However, we primarily show that they
associate a new zeta function, the topological zeta function, to a fractal
string in order to take into account the topology of its fractal boundary. This
expands upon the geometric information garnered by the traditional geometric
zeta function of a fractal string in the theory of complex dimensions. In
particular, one can distinguish between a fractal string whose boundary is the
classical Cantor set, and one whose boundary has a single limit point but has
the same sequence of lengths as the complement of the Cantor set. Later work
will address related, but somewhat different, approaches to multifractals
themselves, via zeta functions, partly motivated by the present paper.Comment: 32 pages, 9 figures. This revised version contains new sections and
figures illustrating the main results of this paper and recent results from
others. Sections 0, 2, and 6 have been significantly rewritte
Electron-electron interactions in one- and three-dimensional mesoscopic disordered rings: a perturbative approach
We have computed persistent currents in a disordered mesoscopic ring in the
presence of small electron-electron interactions, treated in first order
perturbation theory. We have investigated both a contact (Hubbard) and a
nearest neighbour interaction in 1D and 3D. Our results show that a repulsive
Hubbard interaction produces a paramagnetic contribution to the average current
(whatever the dimension) and increases the value of the typical current. On the
other hand, a nearest neighbour repulsive interaction results in a diamagnetic
contribution in 1D and paramagnetic one in 3D, and tends to decrease the value
of the typical current in any dimension. Our study is based on numerical
simulations on the Anderson model and is justified analytically in the presence
of very weak disorder. We have also investigated the influence of the amount of
disorder and of the statistical (canonical or grand-canonical) ensemble.Comment: 7 pages in REVTEX, 4 figure
Dynamic response of isolated Aharonov-Bohm rings coupled to an electromagnetic resonator
We have measured the flux dependence of both real and imaginary conductance
of isolated mesoscopic rings at 310 MHz. The rings are coupled to
a highly sensitive electromagnetic superconducting micro-resonator and lead to
a perturbation of the resonance frequency and quality factor. This experiment
provides a new tool for the investigation of the conductance of mesoscopic
systems without any connection to invasive probes. It can be compared with
recent theoretical predictions emphasizing the differences between isolated and
connected geometries and the relation between ac conductance and persistent
currents. We observe periodic oscillations on both components of the
magnetoconductance. The oscillations of the imaginary conductance whose sign
corresponds to diamagnetism in zero field, are 3 times larger than the Drude
conductance . The real part of the periodic magnetoconductance is of the
order of and is apparently negative in low field. It is thus notably
different from the weak localisation oscillations observed in connected rings,
which are much smaller and opposite in sign.Comment: 4 pages, revtex, epsf, 4 Postscript file
Genetic and Functional Assessment of the Role of the rs13431652-A and rs573225-A Alleles in the G6PC2 Promoter That Are Strongly Associated With Elevated Fasting Glucose Levels
OBJECTIVE Genome-wide association studies have identified a single nucleotide polymorphism (SNP), rs560887, located in a G6PC2 intron that is highly correlated with variations in fasting plasma glucose (FPG). G6PC2 encodes an islet-specific glucose-6-phosphatase catalytic subunit. This study examines the contribution of two G6PC2 promoter SNPs, rs13431652 and rs573225, to the association signal. RESEARCH DESIGN AND METHODS We genotyped 9,532 normal FPG participants (FPG <6.1 mmol/l) for three G6PC2 SNPs, rs13431652 (distal promoter), rs573225 (proximal promoter), rs560887 (3rd intron). We used regression analyses adjusted for age, sex, and BMI to assess the association with FPG and haplotype analyses to assess comparative SNP contributions. Fusion gene and gel retardation analyses characterized the effect of rs13431652 and rs573225 on G6PC2 promoter activity and transcription factor binding. RESULTS Genetic analyses provide evidence for a strong contribution of the promoter SNPs to FPG variability at the G6PC2 locus (rs13431652: β = 0.075, P = 3.6 × 10−35; rs573225 β = 0.073 P = 3.6 × 10−34), in addition to rs560887 (β = 0.071, P = 1.2 × 10−31). The rs13431652-A and rs573225-A alleles promote increased NF-Y and Foxa2 binding, respectively. The rs13431652-A allele is associated with increased FPG and elevated promoter activity, consistent with the function of G6PC2 in pancreatic islets. In contrast, the rs573225-A allele is associated with elevated FPG but reduced promoter activity. CONCLUSIONS Genetic and in situ functional data support a potential role for rs13431652, but not rs573225, as a causative SNP linking G6PC2 to variations in FPG, though a causative role for rs573225 in vivo cannot be ruled out
Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Identification of Mycobacteria in Routine Clinical Practice
Background: Non-tuberculous mycobacteria recovered from respiratory tract specimens are emerging confounder organisms for the laboratory diagnosis of tuberculosis worldwide. There is an urgent need for new techniques to rapidly identify mycobacteria isolated in clinical practice. Matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF MS) has previously been proven to effectively identify mycobacteria grown in high-concentration inocula from collections. However, a thorough evaluation of its use in routine laboratory practice has not been performed. Methodology: We set up an original protocol for the MALDI-TOF MS identification of heat-inactivated mycobacteria after dissociation in Tween-20, mechanical breaking of the cell wall and protein extraction with formic acid and acetonitrile. By applying this protocol to as few as 10 5 colony-forming units of reference isolates of Mycobacterium tuberculosis, Mycobacterium avium, and 20 other Mycobacterium species, we obtained species-specific mass spectra for the creation of a local database. Using this database, our protocol enabled the identification by MALDI-TOF MS of 87 M. tuberculosis, 25M. avium and 12 non-tuberculosis clinical isolates with identification scores $2 within 2.5 hours. Conclusions: Our data indicate that MALDI-TOF MS can be used as a first-line method for the routine identification of heatinactivated mycobacteria. MALDI-TOF MS is an attractive method for implementation in clinical microbiology laboratories i
Magnetic and Electronic Properties of Metal-Atom Adsorbed Graphene
We systematically investigate the magnetic and electronic properties of
graphene adsorbed with diluted 3d-transition and noble metal atoms using first
principles calculation methods. We find that most transition metal atoms (i.e.
Sc, Ti, V, Mn, Fe) favor the hollow adsorption site, and the interaction
between magnetic adatoms and \pi-orbital of graphene induces sizable exchange
field and Rashba spin-orbit coupling, which together open a nontrivial bulk gap
near the Dirac points leading to the quantum-anomalous Hall effect. We also
find that the noble metal atoms (i.e. Cu, Ag, Au) prefer the top adsorption
site, and the dominant inequality of the AB sublattice potential opens another
kind of nontrivial bulk gap exhibiting the quantum-valley Hall effect.Comment: Submitted to PRL on Aug. 10, 2011. 11 pages(4.5 pages for the main
text and 6.5 pages for the supporting materials
Supplement: "Localization and broadband follow-up of the gravitational-wave transient GW150914" (2016, ApJL, 826, L13)
This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands
Revisitando a "epistemologia social": esboço de uma ecologia sociotécnica do trabalho intelectual
A geografia médica e as expedições francesas para o Brasil: uma descrição da estação naval do Brasil e da Prata (1868-1870)
Localization and Broadband Follow-up of the Gravitational-wave Transient GW150914
A gravitational-wave (GW) transient was identified in data recorded by
the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO)
detectors on 2015 September 14. The event, initially designated G184098
and later given the name GW150914, is described in detail elsewhere. By
prior arrangement, preliminary estimates of the time, significance, and
sky location of the event were shared with 63 teams of observers
covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths
with ground- and space-based facilities. In this Letter we describe the
low-latency analysis of the GW data and present the sky localization of
the first observed compact binary merger. We summarize the follow-up
observations reported by 25 teams via private Gamma-ray Coordinates
Network circulars, giving an overview of the participating facilities,
the GW sky localization coverage, the timeline, and depth of the
observations. As this event turned out to be a binary black hole merger,
there is little expectation of a detectable electromagnetic (EM)
signature. Nevertheless, this first broadband campaign to search for a
counterpart of an Advanced LIGO source represents a milestone and
highlights the broad capabilities of the transient astronomy community
and the observing strategies that have been developed to pursue neutron
star binary merger events. Detailed investigations of the EM data and
results of the EM follow-up campaign are being disseminated in papers by
the individual teams.
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