1,743 research outputs found
Common-reflection-surface imaging of shallow and ultrashallow reflectors
We analyzed the feasibility of the common-reflection-surface
(CRS) stack for near-surface surveys as an alternative to the conventional
common midpoint (CMP) stacking procedure. The
data-driven, less user-interactive CRS method could be more
cost efficient for shallow surveys, where the high sensitivity
to velocity analysis makes data processing a critical step. We
compared the results for two field data sets collected to image
shallow and ultrashallow reflectors: an example of shallow Pwave
reflection for targets in the first few hundred meters,
and an example of SH-wave reflection for targets in the first
10 m. By processing the shallow P-wave records using the
CMP method, we imaged several nearly horizontal reflectors
with onsets from 60 to about 250 ms. The CRS stack produced
a stacked section more suited for a subsurface interpretation,
without any preliminary formal and time-consuming velocity analysis, because the imaged reflectors possessed greater coherency
and lateral continuity. With CMP processing of the SHwave
records, we imaged a dipping bedrock interface below
four horizontal reflectors in unconsolidated, very low velocity
sediments. The vertical and lateral resolution was very high, despite
the very shallow depth: the image showed the pinchout of
two layers at less than 10 m depth. The numerous traces used by
the CRS stack improved the continuity of the shallowest reflector,
but the deepest overburden reflectors appear unresolved,
with not well-imaged pinchouts. Using the kinematic wavefield
attributes determined for each stacking operation, we retrieved
velocity fields fitting the stacking velocities we had estimated in
the CMP processing. The use of CRS stack could be a significant
step ahead to increase the acceptance of the seismic reflection
method as a routine investigation method in shallow and
ultrashallow seismics
Generalized multi-photon quantum interference
Non-classical interference of photons lies at the heart of optical quantum
information processing. This effect is exploited in universal quantum gates as
well as in purpose-built quantum computers that solve the BosonSampling
problem. Although non-classical interference is often associated with perfectly
indistinguishable photons this only represents the degenerate case, hard to
achieve under realistic experimental conditions. Here we exploit tunable
distinguishability to reveal the full spectrum of multi-photon non-classical
interference. This we investigate in theory and experiment by controlling the
delay times of three photons injected into an integrated interferometric
network. We derive the entire coincidence landscape and identify transition
matrix immanants as ideally suited functions to describe the generalized case
of input photons with arbitrary distinguishability. We introduce a compact
description by utilizing a natural basis which decouples the input state from
the interferometric network, thereby providing a useful tool for even larger
photon numbers
Completeness of the SO(4) Extended Bethe Ansatz for the One-Dimensional Hubbard Model
We show how to construct a complete set of eigenstates of the hamiltonian of
the one-dimensional Hubbard model on a lattice of even length . This is done
by using the nested Bethe Ansatz {\it and} the symmetry of the model.
We discuss in detail how the counting of independent eigenstates is carried
out.Comment: 33 pages, using latex, to appear in Nucl.Phys. B (FS
Communities of wood-inhabiting bryophytes and fungi on dead beech logs in Europe - reflecting substrate quality or shaped by climate and forest conditions?
Aim: Fungi are drivers of wood decay in forested ecosystem, while bryophytes use dead wood as a platform for their autotrophic lifestyle. We tested the hypothesis that fungal communities on beech logs are mainly structured by substrate quality, while bryophyte communities are structured by climatic gradients. In addition, we tested whether community structure in both organism groups is altered along a gradient from nearly pristine forest to forests heavily affected by management and human disturbance in the past. Location: Europe. Methods: We surveyed 1207 fallen beech logs in 26 of the best-preserved forest stands across six European countries, representing a gradient in overall naturalness of the forest landscape. Recorded species were classified into ecological guilds. Indirect ordination and variation partitioning was used to analyse the relationship between species composition and environmental variables, recorded at log or site level. Results: In total, 10,367 bryophyte and 15,575 fungal records were made, representing 157 and 272 species, respectively. Fungal communities were more clearly structured by substrate quality than were bryophyte communities. In both groups a distinct turnover in species composition was evident along a longitudinal gradient from Central to Western Europe. Fungi specialized in trunk rot and specialized epixylic bryophytes were scarcely represented in Atlantic regions, and partly replaced by species belonging to less specialized guilds. Variables related to climate and forest conditions were confounded along this main geographical gradient in community composition. Main conclusions: We found that bryophyte and fungal communities co-occurring on fallen beech logs in European beech forest reserves differed in their responses to biogeographical drivers and local-scale habitat filters. Both groups responded to major gradients in climate and forest conditions, but the loss of specialist guilds in degraded forest landscapes points to a functionally important effect of forest landscape degradation at the European continental scale. © 2014 John Wiley & Sons Ltd
A Class of Parameter Dependent Commuting Matrices
We present a novel class of real symmetric matrices in arbitrary dimension
, linearly dependent on a parameter . The matrix elements satisfy a set
of nontrivial constraints that arise from asking for commutation of pairs of
such matrices for all , and an intuitive sufficiency condition for the
solvability of certain linear equations that arise therefrom. This class of
matrices generically violate the Wigner von Neumann non crossing rule, and is
argued to be intimately connected with finite dimensional Hamiltonians of
quantum integrable systems.Comment: Latex, Added References, Typos correcte
Scattering Matrix and Excitation Spectrum of the Hubbard Model
We consider the one-dimensional Hubbard model at half filling. We show that
both excitation spectrum and S-matrix are determined by the SO(4) symmetry of
the model. The complete set of excitations is given by the scattering states
four elementary excitations, which form the fundamental representation of
SO(4). We evaluate the exact S-matrix, which satisfies the Yang-Baxter
relation. The results for the repulsive and attractive Hubbard model are
related by an interchange of spin and charge degrees of freedom.Comment: 8 pages, jyTeX (macro included - just TeX the file) ITP-SB-93-4
Antimicrobial resistance of Salmonella enterica in pork and vegetable servings at pork joints in Kampala, Uganda
The aim of this study was to investigate the prevalence and antimicrobial resistance
of Salmonella enterica subsp. enterica serovars including the presence of shared
plasmids in pork and related fresh vegetables served in pork joints in Kampala,
Uganda. Pork butcheries in three of the five administrative divisions of Kampala were
included for the survey. Samples included raw pork, roasted pork, water, onions,
tomatoes, cabbage, butcher’s hands (swabs), utensils (swabs) and fly midgut
extracts. A total of 693 samples were collected from 77 pork butcheries from June-
October 2014.
Overall 53.2% pork joints had samples positive for Salmonella enterica subsp.
enterica serovars. Isolation rates ranged from 31.2% (24/77) for raw pork, 1.3%
(1/77) for roasted pork, 7.8% (6/77) for tomatoes, 2.6% (2/77) for onions, 5.2% (4/77)
for cabbage, 9.1% (7/77) in water, and 22.1% (17/77) from fly midguts. Swab
samples taken from utensil and butcher’s hands swabs were found negative
(Heilmann et al., 2015).
In the isolates obtained, resistance towards 22 antibiotics was tested. Resistances
were found towards 11 out of the 22 antibiotics tested. High resistances were found
to Cephazolin (97%), Cefotixime (93%), Gentamicin (88%), and Ceftazidime (86%).
Intermediate resistance was found to Ciprofloxacin (59%) and Amoxicillin-Clavulanic
acid (57.6%). Most isolates (85%) were susceptible to Levofloxacin, Ofloxacin,
Sulfamethoxazole and Trimethoprim. Identification of plasmids by PCR-based
replicon typing was performed recognizing FIA,FIB,FIC,HI1,HI2,I1-
1ᵞ,L/M,N,P,W,T,A/C,K,B/O,X,Y,F and FIIA. Six incompatibility groups were identified:
FIA, W, FIC, FIB, P, Y with more than one incompatibility group existing among
different isolates.
A high resistance rate among Salmonella strains was found while the total number of
incompatibility groups detected was with approximation 2.4. Thus, even though the
total number of plasmids per strain is low, resistance rates detected remain high. The
high resistance rates are probably resulting from intensified food animal production
driving a greater use of antibiotics, which is a crucial aspect of public health concern
Fermionic R-Operator and Integrability of the One-Dimensional Hubbard Model
We propose a new type of the Yang-Baxter equation (YBE) and the decorated
Yang-Baxter equation (DYBE). Those relations for the fermionic R-operator were
introduced recently as a tool to treat the integrability of the fermion models.
Using the YBE and the DYBE for the XX fermion model, we construct the fermionic
R-operator for the one-dimensional (1D) Hubbard model. It gives another proof
of the integrability of the 1D Hubbard model. Furthermore a new approach to the
SO(4) symmetry of the 1D Hubbard model is discussed.Comment: 25 page
The fecal microbiome in dogs with acute diarrhea and idiopathic inflammatory bowel disease.
Recent molecular studies have revealed a highly complex bacterial assembly in the canine intestinal tract. There is mounting evidence that microbes play an important role in the pathogenesis of acute and chronic enteropathies of dogs, including idiopathic inflammatory bowel disease (IBD). The aim of this study was to characterize the bacterial microbiota in dogs with various gastrointestinal disorders. Fecal samples from healthy dogs (n = 32), dogs with acute non-hemorrhagic diarrhea (NHD; n = 12), dogs with acute hemorrhagic diarrhea (AHD; n = 13), and dogs with active (n = 9) and therapeutically controlled idiopathic IBD (n = 10) were analyzed by 454-pyrosequencing of the 16S rRNA gene and qPCR assays. Dogs with acute diarrhea, especially those with AHD, had the most profound alterations in their microbiome, as significant separations were observed on PCoA plots of unweighted Unifrac distances. Dogs with AHD had significant decreases in Blautia, Ruminococcaceae including Faecalibacterium, and Turicibacter spp., and significant increases in genus Sutterella and Clostridium perfringens when compared to healthy dogs. No significant separation on PCoA plots was observed for the dogs with IBD. Faecalibacterium spp. and Fusobacteria were, however, decreased in the dogs with clinically active IBD, but increased during time periods of clinically insignificant IBD, as defined by a clinical IBD activity index (CIBDAI). Results of this study revealed a bacterial dysbiosis in fecal samples of dogs with various GI disorders. The observed changes in the microbiome differed between acute and chronic disease states. The bacterial groups that were commonly decreased during diarrhea are considered to be important short-chain fatty acid producers and may be important for canine intestinal health. Future studies should correlate these observed phylogenetic differences with functional changes in the intestinal microbiome of dogs with defined disease phenotypes
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