7,369 research outputs found
Patterned Irradiation of YBa_2Cu_3O_(7-x) Thin Films
We present a new experiment on YBa_2Cu_3O_{7-x} (YBCO) thin films using
spatially resolved heavy ion irradiation. Structures consisting of a periodic
array of strong and weak pinning channels were created with the help of metal
masks. The channels formed an angle of +/-45 Deg with respect to the symmetry
axis of the photolithographically patterned structures. Investigations of the
anisotropic transport properties of these structures were performed. We found
striking resemblance to guided vortex motion as it was observed in YBCO single
crystals containing an array of unidirected twin boundaries. The use of two
additional test bridges allowed to determine in parallel the resistivities of
the irradiated and unirradiated parts as well as the respective current-voltage
characteristics. These measurements provided the input parameters for a
numerical simulation of the potential distribution of the Hall patterning. In
contrast to the unidirected twin boundaries in our experiment both strong and
weak pinning regions are spatially extended. The interfaces between
unirradiated and irradiated regions therefore form a Bose-glass contact. The
experimentally observed magnetic field dependence of the transverse voltage
vanishes faster than expected from the numerical simulation and we interpret
this as a hydrodynamical interaction between a Bose-glass phase and a vortex
liquid.Comment: 7 pages, 8 Eps figures included. Submitted to PR
Inferring decoding strategy from choice probabilities in the presence of noise correlations
The activity of cortical neurons in sensory areas covaries with perceptual decisions, a relationship often quantified by choice probabilities. While choice probabilities have been measured extensively, their interpretation has remained fraught with difficulty. Here, we derive the mathematical relationship between choice probabilities, read-out weights and noise correlations within the standard neural decision making model. Our solution allows us to prove and generalize earlier observations based on numerical simulations, and to derive novel predictions. Importantly, we show how the read-out weight profile, or decoding strategy, can be inferred from experimentally measurable quantities. Furthermore, we present a test to decide whether the decoding weights of individual neurons are optimal, even without knowing the underlying noise correlations. We confirm the practical feasibility of our approach using simulated data from a realistic population model. Our work thus provides the theoretical foundation for a growing body of experimental results on choice probabilities and correlations
CII, CI, and CO in the massive star forming region W3 Main
We have used the KOSMA 3m telescope to map the core 7'x5' of the Galactic
massive star forming region W3Main in the two fine structure lines of atomic
carbon and four mid-J transitions of CO and 13CO. In combination with a map of
singly ionized carbon (Howe et al. 1991), and FIR fine structure line data
observed by ISO/LWS at the center position, these data sets allow to study in
detail the physical structure of the photon dominated cloud interface regions
(PDRs) where the occurance of carbon changes from CII to CI, and to CO.Comment: 4 pages, 4 figures, to appear in "Proceedings of the 4th
Cologne-Bonn-Zermatt-Symposium, The dense interstellar medium in galaxies",
eds. S. Pfalzner, C. Kramer, C. Straubmeier, and A. Heithausen (Springer
Verlag
Epitaxial film growth and magnetic properties of Co_2FeSi
We have grown thin films of the Heusler compound Co_2FeSi by RF magnetron
sputtering. On (100)-oriented MgO substrates we find fully epitaxial
(100)-oriented and L2_1 ordered growth. On Al_2O_3 (11-20) substrates, the film
growth is (110)-oriented, and several in-plane epitaxial domains are observed.
The temperature dependence of the electrical resistivity shows a power law with
an exponent of 7/2 at low temperatures. Investigation of the bulk magnetic
properties reveals an extrapolated saturation magnetization of 5.0 mu_B/fu at 0
K. The films on Al_2O_3 show an in-plane uniaxial anisotropy, while the
epitaxial films are magnetically isotropic in the plane. Measurements of the
X-ray magnetic circular dichroism of the films allowed us to determine element
specific magnetic moments. Finally we have measured the spin polarization at
the surface region by spin-resolved near-threshold photoemission and found it
strongly reduced in contrast to the expected bulk value of 100%. Possible
reasons for the reduced magnetization are discussed.Comment: 9 pages, 12 figure
Ploidy composition in all-hybrid frog populations in relation to ecological conditions
Question: What explains the differences in ratios of diploid (LR) and two types of triploid
frogs (LLR, LRR) among all-hybrid frog populations?
Hypothesis: Ecological conditions favouring one (LL) or the other (RR) parental species also
favour those triploids that carry two copies of the respective genome (dosage effect), whereas
diploids dominate under intermediate conditions.
Organism: European water frog (Pelophylax esculentus).
Field site: Thirty-four natural ponds in the province of Skåne, southern Sweden.
Methods: We caught more than 3000 frogs, determined their genotypes with microsatellites,
and related the ploidy composition to several uncorrelated ecological parameters, including
pond morphology, vegetation, and physical and chemical water parameters.
Conclusions: We found a shift from predominantly LLR in small isolated ponds to more LRR
in large wetland ponds. This parallels the preferences of the parental species LL and RR
for small and large bodies of water, respectively. The effects that pond vegetation and
physico-chemical water parameters exert on the parental species were not found in all-hybrid
populations. This suggests that environmental parameters affect the genotype composition of
all-hybrid populations less than populations containing the parental species. Pond-to-pond
differences in LR, LLR, and LRR proportions seem to be better explained by differences in
gamete production and thus inheritance patterns
Geometric Modular Action, Wedge Duality and Lorentz Covariance are Equivalent for Generalized Free Fields
The Tomita-Takesaki modular groups and conjugations for the observable
algebras of space-like wedges and the vacuum state are computed for
translationally covariant, but possibly not Lorentz covariant, generalized free
quantum fields in arbitrary space-time dimension d. It is shown that for the condition of geometric modular action (CGMA) of Buchholz, Dreyer, Florig
and Summers \cite{BDFS}, Lorentz covariance and wedge duality are all
equivalent in these models. The same holds for d=3 if there is a mass gap. For
massless fields in d=3, and for d=2 and arbitrary mass, CGMA does not imply
Lorentz covariance of the field itself, but only of the maximal local net
generated by the field
Shift of the surface-barrier part of the irreversibility line due to columnar defects in Bi_2Sr_2CaCu_2O_8 thin films
We report the results of studying the influence of the uranium-ion
irradiation of the Bi_2Sr_2CaCu_2O_8 thin films on the high-temperature part
(close to critical temperature) of their irreversibility line. We studied
irreversible properties of the films by measuring the hysteresis of nonresonant
microwave absorption. The results have revealed the shift of irreversibility
line towards low temperatures and magnetic fields. The effect is most
significant for the films irradiated with large doses, more than 1T. This fact
is in good agreement with the theoretical prediction by Koshelev and Vinokur of
suppression of surface barrier by columnar defects.Comment: LaTeX2e, 9 pages with 3 figures, to be published in Physica
A perturbative approach to decays into two mesons
The modified perturbative approach in which transverse degrees of freedom as
well as Sudakov suppressions are taken into account, is applied to decays
into two mesons. The influence of various model parameters (CKM matrix
elements, decay constant, mesonic wave functions) on the results as well as
short distance corrections to the weak Hamiltonian are discussed in some
detail. The perturbative contributions to the decays yield branching ratios
of the order of which values are well below the upper
limit for the branching ratio as measured by CLEO.Comment: 26 pages, RevTex, 6 figures appended (compressed and uuencode using
'uufiles'
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MicroRNA regulation of type 2 innate lymphoid cell homeostasis and function in allergic inflammation.
MicroRNAs (miRNAs) exert powerful effects on immunity through coordinate regulation of multiple target genes in a wide variety of cells. Type 2 innate lymphoid cells (ILC2s) are tissue sentinel mediators of allergic inflammation. We established the physiological requirements for miRNAs in ILC2 homeostasis and immune function and compared the global miRNA repertoire of resting and activated ILC2s and T helper type 2 (TH2) cells. After exposure to the natural allergen papain, mice selectively lacking the miR-17∼92 cluster in ILC2s displayed reduced lung inflammation. Moreover, miR-17∼92-deficient ILC2s exhibited defective growth and cytokine expression in response to IL-33 and thymic stromal lymphopoietin in vitro. The miR-17∼92 cluster member miR-19a promoted IL-13 and IL-5 production and inhibited expression of several targets, including SOCS1 and A20, signaling inhibitors that limit IL-13 and IL-5 production. These findings establish miRNAs as important regulators of ILC2 biology, reveal overlapping but nonidentical miRNA-regulated gene expression networks in ILC2s and TH2 cells, and reinforce the therapeutic potential of targeting miR-19 to alleviate pathogenic allergic responses
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