Limits on Superconductivity-Related Magnetization in Sr2_2RuO4_4 and PrOs4_4Sb12_{12} from Scanning SQUID Microscopy

We present scanning SQUID microscopy data on the superconductors Sr2RuO4 (Tc = 1.5 K) and PrOs$_4$Sb$_{12}$ (Tc = 1.8 K). In both of these materials, superconductivity-related time-reversal symmetry-breaking fields have been observed by muon spin rotation; our aim was to visualize the structure of these fields. However in neither Sr$_2$RuO$_4$ nor PrOs$_4$Sb$_{12}$ do we observe spontaneous superconductivity-related magnetization. In Sr$_2$RuO$_4$, many experimental results have been interpreted on the basis of a $px \pm ipy$ superconducting order parameter. This order parameter is expected to give spontaneous magnetic induction at sample edges and order parameter domain walls. Supposing large domains, our data restrict domain wall and edge fields to no more than ~0.1% and ~0.2% of the expected magnitude, respectively. Alternatively, if the magnetization is of the expected order, the typical domain size is limited to ~30 nm for random domains, or ~500 nm for periodic domains.Comment: 8 pages, 7 figures. Submitted to Phys. Rev.

Evidence for Nodal Superconductivity in LaFePO from Scanning SQUID Susceptometry

We measure changes in the penetration depth $\lambda$ of the $T_c \approx 6$ K superconductor LaFePO. In the process scanning SQUID susceptometry is demonstrated as a technique for accurately measuring {\it local} temperature-dependent changes in $\lambda$, making it ideal for studying early or difficult-to-grow materials. $\lambda$ of LaFePO is found to vary linearly with temperature from 0.36 to $\sim$2 K, with a slope of 143$\pm$15 \AA/K, suggesting line nodes in the superconducting order parameter. The linear dependence up to $\sim T_c/3$ is similar to the cuprate superconductors, indicating well-developed nodes.Comment: 4 pages, 5 figure

Magnetoresistance of UPt3

We have performed measurements of the temperature dependence of the magnetoresistance up to 9 T in bulk single crystals of UPt3 with the magnetic field along the b axis, the easy magnetization axis. We have confirmed previous results for transverse magnetoresistance with the current along the c axis, and report measurements of the longitudinal magnetoresistance with the current along the b axis. The presence of a linear term in both cases indicates broken orientational symmetry associated with magnetic order. With the current along the c axis the linear term appears near 5 K, increasing rapidly with decreasing temperature. For current along the b axis the linear contribution is negative.Comment: 6 pages, 3 figures, submitted to Quantum Fluids and Solids Conference (QFS 2006

Dendritic Spine Shape Analysis: A Clustering Perspective

Functional properties of neurons are strongly coupled with their morphology. Changes in neuronal activity alter morphological characteristics of dendritic spines. First step towards understanding the structure-function relationship is to group spines into main spine classes reported in the literature. Shape analysis of dendritic spines can help neuroscientists understand the underlying relationships. Due to unavailability of reliable automated tools, this analysis is currently performed manually which is a time-intensive and subjective task. Several studies on spine shape classification have been reported in the literature, however, there is an on-going debate on whether distinct spine shape classes exist or whether spines should be modeled through a continuum of shape variations. Another challenge is the subjectivity and bias that is introduced due to the supervised nature of classification approaches. In this paper, we aim to address these issues by presenting a clustering perspective. In this context, clustering may serve both confirmation of known patterns and discovery of new ones. We perform cluster analysis on two-photon microscopic images of spines using morphological, shape, and appearance based features and gain insights into the spine shape analysis problem. We use histogram of oriented gradients (HOG), disjunctive normal shape models (DNSM), morphological features, and intensity profile based features for cluster analysis. We use x-means to perform cluster analysis that selects the number of clusters automatically using the Bayesian information criterion (BIC). For all features, this analysis produces 4 clusters and we observe the formation of at least one cluster consisting of spines which are difficult to be assigned to a known class. This observation supports the argument of intermediate shape types.Comment: Accepted for BioImageComputing workshop at ECCV 201

Local measurement of the penetration depth in the pnictide superconductor Ba(Fe0.95_{0.95}Co0.05_{0.05})2_2As2_2

We use magnetic force microscopy (MFM) and scanning SQUID susceptometry to measure the local superfluid density $\rho_{s}$ in Ba(Fe$_{0.95}$Co$_{0.05}$)$_2$As$_2$ single crystals from 0.4 K to the critical temperature $T_c=18.5$ K. We observe that the penetration depth $\lambda$ varies about ten times more slowly with temperature than previously published, with a dependence that can be well described by a clean two-band fully gapped model. We demonstrate that MFM can measure the important and hard-to-determine absolute value of $\lambda$, as well as obtain its temperature dependence and spatial homogeneity. We find $\rho_{s}$ to be uniform despite the highly disordered vortex pinning

Local measurement of the superfluid density in the pnictide superconductor Ba(Fe1−x_{1-x}Cox_{x})2_2As2_2 across the superconducting dome

We measure the penetration depth $\lambda_{ab}(T)$ in Ba(Fe$_{1-x}$Co$_{x}$)$_2$As$_2$ using local techniques that do not average over the sample. The superfluid density $\rho_s(T)\equiv1/\lambda_{ab}(T)^2$ has three main features. First, $\rho_s(T=0)$ falls sharply on the underdoped side of the dome. Second, $\lambda_{ab}(T)$ is flat at low $T$ at optimal doping, indicating fully gapped superconductivity, but varies more strongly in underdoped and overdoped samples, consistent with either a power law or a small second gap. Third, $\rho_s(T)$ varies steeply near $T_c$ for optimal and underdoping. These observations are consistent with an interplay between magnetic and superconducting phases

Interplay between magnetism and superconductivity and appearance of a second superconducting transition in alpha-FeSe at high pressure

We synthesized tetragonal alpha-FeSe by melting a powder mixture of iron and selenium at high pressure. Subsequent annealing at normal pressure results in removing traces of hexagonal beta- FeSe, formation of a rather sharp transition to superconducting state at Tc ~ 7 K, and the appearance of a magnetic transition near Tm = 120 K. Resistivity and ac-susceptibility were measured on the annealed sample at hydrostatic pressure up to 4.5 GPa. A magnetic transition visible in ac-susceptibility shifts down under pressure and the resistive anomaly typical for a spin density wave (SDW) antiferromagnetic transition develops near the susceptibility anomaly. Tc determined by the appearance of a diamagnetic response in susceptibility, increases linearly under pressure at a rate dTc/dP = 3.5 K/GPa. Below 1.5 GPa, the resistive superconducting transition is sharp; the width of transition does not change with pressure; and, Tc determined by a peak in drho/dT increases at a rate ~ 3.5 K/GPa. At higher pressure, a giant broadening of the resistive transition develops. This effect cannot be explained by possible pressure gradients in the sample and is inherent to alpha-FeSe. The dependences drho(T)/dT show a signature for a second peak above 3 GPa which is indicative of the appearance of another superconducting state in alpha-FeSe at high pressure. We argue that this second superconducting phase coexists with SDW antiferromagnetism in a partial volume fraction and originates from pairing of charge carriers from other sheets of the Fermi surface

Good Friends, Bad News - Affect and Virality in Twitter

The link between affect, defined as the capacity for sentimental arousal on the part of a message, and virality, defined as the probability that it be sent along, is of significant theoretical and practical importance, e.g. for viral marketing. A quantitative study of emailing of articles from the NY Times finds a strong link between positive affect and virality, and, based on psychological theories it is concluded that this relation is universally valid. The conclusion appears to be in contrast with classic theory of diffusion in news media emphasizing negative affect as promoting propagation. In this paper we explore the apparent paradox in a quantitative analysis of information diffusion on Twitter. Twitter is interesting in this context as it has been shown to present both the characteristics social and news media. The basic measure of virality in Twitter is the probability of retweet. Twitter is different from email in that retweeting does not depend on pre-existing social relations, but often occur among strangers, thus in this respect Twitter may be more similar to traditional news media. We therefore hypothesize that negative news content is more likely to be retweeted, while for non-news tweets positive sentiments support virality. To test the hypothesis we analyze three corpora: A complete sample of tweets about the COP15 climate summit, a random sample of tweets, and a general text corpus including news. The latter allows us to train a classifier that can distinguish tweets that carry news and non-news information. We present evidence that negative sentiment enhances virality in the news segment, but not in the non-news segment. We conclude that the relation between affect and virality is more complex than expected based on the findings of Berger and Milkman (2010), in short 'if you want to be cited: Sweet talk your friends or serve bad news to the public'.Comment: 14 pages, 1 table. Submitted to The 2011 International Workshop on Social Computing, Network, and Services (SocialComNet 2011

Mastectomy versus radiotherapy as treatment for stage I-II breast cancer: A prospective randomized trial at the National Cancer Institute

In 1979, the National Cancer Institute in Bethesda, Maryland initiated a randomized, prospective trial to compare surgery versus radiation therapy in the treatment of stages I and II breast cancer. Surgical treatment consists of total mastectomy with axillary lymph node dissection (modified radical mastectomy) and breast reconstruction; radiation treatment consists of gross tumor excision, axillary lymph node dissection, and comprehensive irradiation including a boost dose to the tumor bed. All patients with pathologically positive axillary nodes receive 11 cycles of adjuvant Adriamycin ® /Cytoxan ® chemotherapy. As of December 1984, there have been 175 patients entered in the study. Twenty-three patients have developed disease recurrence (12 mastectomy, 11 radiation), but it is too early to obtain definitive treatment-related results. En 1979 l'Institut National du Cancer de Bethesda a lancé une étude prospective randomisée permettant de comparer les résultats respectifs de la chirurgie et de la radiothérapie en ce qui concerne les stades I et II du cancer du sein. Le traitement chirurgical consiste en la mastectomie totale complétée par le curage ganglionnaire axillaire (mastectomie totale modifiée); le traitement dit radiothérapique consiste en l'exérèse large de la tumeur associée au curage ganglionnaire axillaire et à l'administration d'une dose élevée de rayons au niveau du lit tumoral. Toutes les opérées dont les ganglions sont envahis reçoivent en outre 11 cycles d'une combinaison d'Adriamycine et Cytoxan. De 1979 à Décembre 1984, 175 malades ont fait l'objet de cette étude. Vingt-trois ont accusé une récidive (12 après mastectomie et 11 après traitement dit radiothérapique) mais il est encore trop tôt pour tirer des conclusions définitives de ces résultats. El Instituto Nacional de Cáncer de Bethesda inició en 1979 un ensayo prospectivo y aleatorio orientado a comparar el tratamiento quirúrgico versus radioterapia en el manejo del cáncer mamario en estados I y II. El tratamiento quirúrgico consistió de mastectomía total con disección ganglionar axilar (mastectomía radical modificada) y reconstrucción mamaria; el manejo radioterapéutico consistió de resección del tumor, disección de los ganglios linfáticos axilares e irradiación comprensiva incluyendo una dosis de refuerzo al lecho tumoral. Todos los pacientes con ganglios axilares histológicamente positivos recibieron 11 ciclos de quimioterapia adyuvante con Adriamicina/Citoxán. Hasta diciembre de 1984, 175 pacientes habían entrado al estudio. Veintitrés pacientes han desarrollado recurrencia de la enfermedad (12 mastectomía, 11 irradiación), pero es todavía muy temprano para derivar resultados definitivos.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41319/1/268_2005_Article_BF01655179.pd