37,245 research outputs found
Synthesis and Study of 10% Ni Doped (YBa2Cu3-xNixOy) High Tc Superconductor
No full textThis study is based on our hypothesis that predicts the possibility of Y–Ba–Ni–O superconductor. A comparative study of Y–Ba–Cu–O and 10% Ni doped Y–Ba–Cu–O (having Tc as high as 84 K) is presented. Resistivity, XRD, oxygen content and Cu–K-XANES measurements are reported
Recommended from our members
Time-Space Tradeoffs for Distinguishing Distributions and Applications to Security of Goldreich’s PRG
No full textIn this work, we establish lower-bounds against memory bounded algorithms for distinguishing between natural pairs of related distributions from samples that arrive in a streaming setting.
Our first result applies to the problem of distinguishing the uniform distribution on {0,1}ⁿ from uniform distribution on some unknown linear subspace of {0,1}ⁿ. As a specific corollary, we show that any algorithm that distinguishes between uniform distribution on {0,1}ⁿ and uniform distribution on an n/2-dimensional linear subspace of {0,1}ⁿ with non-negligible advantage needs 2^Ω(n) samples or Ω(n²) memory (tight up to constants in the exponent).
Our second result applies to distinguishing outputs of Goldreich’s local pseudorandom generator from the uniform distribution on the output domain. Specifically, Goldreich’s pseudorandom generator G fixes a predicate P:{0,1}^k → {0,1} and a collection of subsets S₁, S₂, …, S_m ⊆ [n] of size k. For any seed x ∈ {0,1}ⁿ, it outputs P(x_S₁), P(x_S₂), …, P(x_{S_m}) where x_{S_i} is the projection of x to the coordinates in S_i. We prove that whenever P is t-resilient (all non-zero Fourier coefficients of (-1)^P are of degree t or higher), then no algorithm, with < n^ε memory, can distinguish the output of G from the uniform distribution on {0,1}^m with a large inverse polynomial advantage, for stretch m ≤ (n/t) ^{(1-ε)/36 ⋅ t} (barring some restrictions on k). The lower bound holds in the streaming model where at each time step i, S_i ⊆ [n] is a randomly chosen (ordered) subset of size k and the distinguisher sees either P(x_{S_i}) or a uniformly random bit along with S_i.
An important implication of our second result is the security of Goldreich’s generator with super linear stretch (in the streaming model), against memory-bounded adversaries, whenever the predicate P satisfies the necessary condition of t-resiliency identified in various prior works.
Our proof builds on the recently developed machinery for proving time-space trade-offs (Raz 2016 and follow-ups). Our key technical contribution is to adapt this machinery to work for distinguishing problems in contrast to prior works on similar results for search/learning problems
Direct numerical test of the B-G-K model equation by the DSMC method
No full textIn the present paper the rarefied gas how caused by the sudden change of the wall temperature and the Rayleigh problem are simulated by the DSMC method which has been validated by experiments both in global flour field and velocity distribution function level. The comparison of the simulated results with the accurate numerical solutions of the B-G-K model equation shows that near equilibrium the BG-K equation with corrected collision frequency can give accurate result but as farther away from equilibrium the B-G-K equation is not accurate. This is for the first time that the error caused by the B-G-K model equation has been revealed
G. K. Chesterton Portrait, Detail
No full textThis image is a detail of the oil portrait of the British author G. K. Chesterton (1874–1936), painted by Edwin Swan.https://collected.jcu.edu/chestertonimages/1001/thumbnail.jp
Repetitive transcranial magnetic stimulation (r-TMS) and selective serotonin reuptake inhibitor-resistance in obsessive-compulsive disorder: A meta-analysis and clinical implications
No full textIntroduction: Despite promising results from several randomized controlled trials (RCTs) and meta-analyses, the efficacy of r-TMS as a treatment for OCD remains controversial, at least in part owing to inconsistency in the trial methodologies and heterogeneity in the trial outcomes. This meta-analysis attempts to explain some of this heterogeneity by comparing the efficacy of r-TMS in patients with or without resistance to treatment with selective serotonin reuptake inhibitors (SSRI), defined using standardized criteria. Methods: We conducted a pre-registered (PROSPERO ID: 241381) systematic review and meta-analysis. English language articles reporting blinded RCTs were retrieved from searches using MEDLINE, PsycINFO, and Cochrane Library databases. Studies were subjected to subgroup analysis based on four stages of treatment resistance, defined using an adaptation of published criteria (1 = not treatment resistant, 2 = one SSRI trial failed, 3 = two SSRI trials failed, 4 = two SSRI trials failed plus one or more CBT trial failed). Meta-regression analyses investigated patient and methodological factors (age, duration of OCD, illness severity, stage of treatment-resistance, or researcher allegiance) as possible moderators of effect size. Results: Twenty-five independent comparisons (23 studies) were included. Overall, r-TMS showed a medium-sized reduction of Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) scores (Hedge's g: -0.47; 95%CI: - 0.67 to −0.27) with moderate heterogeneity (I2 = 39.8%). Assessment of publication bias using Trim and Fill analysis suggested a reduced effect size that remained significant (g: -0.29; 95%CI: −0.51 to −0.07). Subgroup analysis found that those studies including patients non-resistant to SSRI (stage 1) (g: -0.65; 95%CI: −1.05 to −0.25, k = 7) or with low SSRI-resistance (stage 2) (g:-0.47; 95%CI: −0.86 to −0.09, k = 6) produced statistically significant results with low heterogeneity, while studies including more highly resistant patients at stage 3 (g: −0.39; 95%CI: −0.90 to 0.11, k = 4) and stage 4 (g: -0.36; 95%CI: −0.75 to 0.03, k = 8) did not. Intriguingly, the only significant moderator of the effect size found by meta-regression was the severity of baseline depressive symptoms. All trials showed evidence of researcher allegiance in favour of the intervention and therefore caution is required in interpreting the reported effect sizes. Conclusion: This meta-analysis shows that r-TMS is an effective treatment for OCD, but largely for those not resistant to SSRI or failing to respond to only one SSRI trial. As a consequence, r-TMS may be best implemented earlier in the care pathway. These findings would have major implications for clinical service development, but further well-powered RCTs, which eliminate bias from researcher allegiance, are needed before definitive conclusions can be drawn
Sampling hurdles : “Borderline Illegitimate” to legitimate data.
No full textIn this paper the author discusses how sampling access and recruitment problems encountered in an in-depth interview study heightened her sensitivity to “borderline illegitimate” data. The term illegitimate data usually refers to the data collected during a covert study, whereas “legitimate” data are collected during an overt study. Hence, data collected during any nonconsented period(s) of an overt study lie on the borderline of illegitimacy and legitimacy, and constitute what the author calls borderline illegitimate data. Such data need legitimization before use. The borderline illegitimate data were collected during the pre- and postinterview stages of her study as they explained how medical and ethnic cultures and sensitivity to racism as a topic combined to create sample recruitment difficulties of the study. The author later legitimized them by sharing them with the participants, guaranteeing anonymity, and asking their permission to use them
XAS Study of Hole Density and Symmetry in a Bi2Sr2CaCu2O8+d Single Crystal
No full textA complete set of polarized XAS spectra at copper L3-, oxygen K- and bismuth L3-edges have been recorded on the same well characterized single crystals of Bi2Sr2CaCu2O8+delta superconductor. The copper L3-edges show clearly the decrease of the 3d9 L line intensity when the electric field E of the incident X-ray beam rotates from the (a, b) plane to the c-axis direction. This result is in agreement with the x, y symmetry of the doping holes as shown by the oxygen K-edges without any ambiguity. The remaining intensity of the main 3d9 line on the copper L3-edge recorded with E parallel to c-axis let us assume that some holes could be created in the 3d3z2-r2 by overlapping with either the oxygen 2p(x,y) or the copper 4s orbitals. As observed before, the bismuth L3-edges show clearly the energy shift of the superconductor spectra towards low energy with respect to Bi(III) references confirming again the [Bi-O]infinity layers as electron reservoir. A maximum of this shift has been observed for E parallel to (a,b) in agreement with the presence of long Bi-O distances and o extra electrons in the bismuth layers
Diversified Top-k Graph Pattern Matching
No full textGraph pattern matching has been widely used in e.g., social data analysis. A number of matching algorithms have been developed that, given a graph pattern Q and a graph G, compute the set M(Q;G) of matches of Q in G. However, these algorithms often return an excessive number of matches, and are expensive on large real-life social graphs. Moreover, in practice many social queries are to find matches of a specific pattern node, rather than the entire M(Q;G). This paper studies top-k graph pattern matching. (1) We revise graph pattern matching defined in terms of simulation, by supporting a designated output node uo. Given G and Q, it is to find those nodes in M(Q;G) that match uo, instead of the large set M(Q;G). (2)We study two classes of functions for ranking the matches: relevance functions r() based on, e.g., social impact, and distance functions d() to cover diverse elements. (3) We develop two algorithms for computing top-k matches of uo based on r(), with the early termination property, i.e., they find top-k matches without computing the entire M(Q;G). (4)We also study diversifiedtop-k matching, a bi-criteria optimization problem based on both r() and d(). We show that its decision problem is NP-complete. Nonetheless, we provide an approximation algorithm with performance guarantees and a heuristic one with the early termination property. (5) Using real-life and synthetic data, we experimentally verify that our (diversified) top-k matching algorithms are effective, and outperform traditional matching algorithms in efficiency
Minimum cost k-trees
No full textEsta dissertação trata do problema da k-árvore de custo mínimo (kMST): dados um grafo conexo G, um custo não-negativo c_e para cada aresta e e um número inteiro positivo k, encontrar uma árvore com k vértices que tenha custo mínimo. O kMST é um problema NP-difícil e portanto não se conhece um algoritmo polinomial para resolvê-lo. Nesta dissertação discutimos alguns casos em que é possível resolver o problema em tempo polinomial. Também são estudados algoritmos de aproximação para o kMST. Entre os algoritmos de aproximação estudados, apresentamos a 2-aproximação desenvolvida por Naveen Garg, que atualmente é o algoritmo com melhor fator de aproximação.This dissertation studies the minimum cost k-tree problem (kMST): given a connected graph G, a nonnegative cost function c_e for each edge e and a positive integer k, find a minimum cost tree with k vertices. The kMST is an NP-hard problem, which implies that it is not known a polynomial algorithm to solve it. In this dissertation we discuss some cases that can be solved in polynomial time. We also study approximation algorithms for the kMST. Among the approximation algorithms we present the 2-approximation developed by Naveen Garg, which is currently the algorithm with the best approximation factor
- …
