156 research outputs found
Extended Coherence Time with Atom-Number Squeezed Sources
Coherence properties of Bose-Einstein condensates offer the potential for
improved interferometric phase contrast. However, decoherence effects due to
the mean-field interaction shorten the coherence time, thus limiting potential
sensitivity. In this work, we demonstrate increased coherence times with number
squeezed states in an optical lattice using the decay of Bloch oscillations to
probe the coherence time. We extend coherence times by a factor of 2 over those
expected with coherent state BEC interferometry. We observe quantitative
agreement with theory both for the degree of initial number squeezing as well
as for prolonged coherence times.Comment: 4 pages, 4 figure
Network Overload due to Massive Attacks
We study the cascading failure of networks due to overload, using the
betweenness centrality of a node as the measure of its load following the
Motter and Lai model. We study the fraction of survived nodes at the end of the
cascade as function of the strength of the initial attack, measured by
the fraction of nodes , which survive the initial attack for different
values of tolerance in random regular and Erd\"os-Renyi graphs. We
find the existence of first order phase transition line on a
plane, such that if the cascade of failures lead to a very
small fraction of survived nodes and the giant component of the network
disappears, while for , is large and the giant component of the
network is still present. Exactly at the function undergoes a
first order discontinuity. We find that the line ends at critical
point ,in which the cascading failures are replaced by a
second order percolation transition. We analytically find the average
betweenness of nodes with different degrees before and after the initial
attack, investigate their roles in the cascading failures, and find a lower
bound for . We also study the difference between a localized and
random attacks
Bostonia: 1998-1999, no. 1, 3-4
Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs
Gravitational Wave Detection with Atom Interferometry
We propose two distinct atom interferometer gravitational wave detectors, one
terrestrial and another satellite-based, utilizing the core technology of the
Stanford atom interferometer presently under construction. The
terrestrial experiment can operate with strain sensitivity in the 1 Hz - 10 Hz band, inaccessible to
LIGO, and can detect gravitational waves from solar mass binaries out to
megaparsec distances. The satellite experiment probes the same frequency
spectrum as LISA with better strain sensitivity . Each configuration compares two widely
separated atom interferometers run using common lasers. The effect of the
gravitational waves on the propagating laser field produces the main effect in
this configuration and enables a large enhancement in the gravitational wave
signal while significantly suppressing many backgrounds. The use of ballistic
atoms (instead of mirrors) as inertial test masses improves systematics coming
from vibrations and acceleration noise, and reduces spacecraft control
requirements.Comment: 5 pages, 5 figures, updated with journal referenc
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Community Service: Editor pride and user preference on local newspaper websites
Armed with readily accessible online traffic logs that provide detailed information about the items users are selecting to view, editors are voicing concern about the potential effect on their own content decisions. Through a survey of local British newspaper editors, this article examines the overlap between user preferences, as suggested by assessments of website traffic, and content that editors identify as their best. Results are considered in the context of two related subsets of agenda-setting theory, as well as the sociological process of “making news.” The study finds overlap between broad categories of stories preferred by editors and users, but a considerable disconnect over the nature of the items within those categories
Stabbing News: Articulating Crime Statistics in the Newsroom
There is a comprehensive body of scholarly work regarding the way media represent crime and how it is constructed in the media narrative as a news item. These works have often suggested that in many cases public anxieties in relation to crime levels are not justified by actual data. However, few works have examined the gathering and dissemination of crime statistics by non-specialist journalists and the way crime statistics are gathered and used in the newsroom. This article seeks to explore in a comparative manner how journalists in newsrooms access and interpret quantitative data when producing stories related to crime. In so doing, the article highlights the problems and limitations of journalists in dealing with crime statistics as a news source, while assessing statistics-related methodologies and skills used in the newsrooms across the United Kingdom when producing stories related to urban crime
Fragile x syndrome and autism: from disease model to therapeutic targets
Autism is an umbrella diagnosis with several different etiologies. Fragile X syndrome (FXS), one of the first identified and leading causes of autism, has been modeled in mice using molecular genetic manipulation. These Fmr1 knockout mice have recently been used to identify a new putative therapeutic target, the metabotropic glutamate receptor 5 (mGluR5), for the treatment of FXS. Moreover, mGluR5 signaling cascades interact with a number of synaptic proteins, many of which have been implicated in autism, raising the possibility that therapeutic targets identified for FXS may have efficacy in treating multiple other causes of autism
Mitochondrial dysfunction in autism spectrum disorders: a systematic review and meta-analysis
A comprehensive literature search was performed to collate evidence of mitochondrial dysfunction in autism spectrum disorders (ASDs) with two primary objectives. First, features of mitochondrial dysfunction in the general population of children with ASD were identified. Second, characteristics of mitochondrial dysfunction in children with ASD and concomitant mitochondrial disease (MD) were compared with published literature of two general populations: ASD children without MD, and non-ASD children with MD. The prevalence of MD in the general population of ASD was 5.0% (95% confidence interval 3.2, 6.9%), much higher than found in the general population (∼0.01%). The prevalence of abnormal biomarker values of mitochondrial dysfunction was high in ASD, much higher than the prevalence of MD. Variances and mean values of many mitochondrial biomarkers (lactate, pyruvate, carnitine and ubiquinone) were significantly different between ASD and controls. Some markers correlated with ASD severity. Neuroimaging, in vitro and post-mortem brain studies were consistent with an elevated prevalence of mitochondrial dysfunction in ASD. Taken together, these findings suggest children with ASD have a spectrum of mitochondrial dysfunction of differing severity. Eighteen publications representing a total of 112 children with ASD and MD (ASD/MD) were identified. The prevalence of developmental regression (52%), seizures (41%), motor delay (51%), gastrointestinal abnormalities (74%), female gender (39%), and elevated lactate (78%) and pyruvate (45%) was significantly higher in ASD/MD compared with the general ASD population. The prevalence of many of these abnormalities was similar to the general population of children with MD, suggesting that ASD/MD represents a distinct subgroup of children with MD. Most ASD/MD cases (79%) were not associated with genetic abnormalities, raising the possibility of secondary mitochondrial dysfunction. Treatment studies for ASD/MD were limited, although improvements were noted in some studies with carnitine, co-enzyme Q10 and B-vitamins. Many studies suffered from limitations, including small sample sizes, referral or publication biases, and variability in protocols for selecting children for MD workup, collecting mitochondrial biomarkers and defining MD. Overall, this evidence supports the notion that mitochondrial dysfunction is associated with ASD. Additional studies are needed to further define the role of mitochondrial dysfunction in ASD
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