10,012 research outputs found
Stable isotope probing: Technical considerations when resolving Âčâ”N-labeled RNA in gradients
RNA based stable isotope probing (SIP) facilitates the detection and identification of active members of microbial populations that are involved in the assimilation of an isotopically labeled compound. Âčâ”N-RNA-SIP is a new method that has been discussed in recent literature but has not yet been tested. Herein, we define the limitations to using Âčâ”N-labeled substrates for SIP and propose modifications to compensate for some of these shortcomings. We have used Âčâ”N-RNA-SIP as a tool for analysing mixed bacterial populations that use nitrogen substrates. After incubating mixed microbial communities with Âčâ”N-ammonium chloride or Âčâ”Nâ we assessed the fractionation resolution of Âčâ”N-RNA by isopycnic centrifugation in caesium trifluoroacetate (CsTFA) gradients. We found that the more isotopic label incorporated, the further the buoyant density (BD) separation between Âčâ”N- and ÂčâŽN-RNA, however it was not possible to resolve the labeled from unlabeled RNA definitively through gradient fractionation. Terminal-restriction fragment length polymorphism (T-RFLP) analysis of the extracted RNA and fluorescent in situ hybridisation (FISH) analysis of the enrichment cultures provided some insight into the organisms involved in nitrogen fixation. This approach is not without its limitations and will require further developments to assess its applicability to other nitrogen-fixing environments
A Block Minorization--Maximization Algorithm for Heteroscedastic Regression
The computation of the maximum likelihood (ML) estimator for heteroscedastic
regression models is considered. The traditional Newton algorithms for the
problem require matrix multiplications and inversions, which are bottlenecks in
modern Big Data contexts. A new Big Data-appropriate minorization--maximization
(MM) algorithm is considered for the computation of the ML estimator. The MM
algorithm is proved to generate monotonically increasing sequences of
likelihood values and to be convergent to a stationary point of the
log-likelihood function. A distributed and parallel implementation of the MM
algorithm is presented and the MM algorithm is shown to have differing time
complexity to the Newton algorithm. Simulation studies demonstrate that the MM
algorithm improves upon the computation time of the Newton algorithm in some
practical scenarios where the number of observations is large
Quantum search without entanglement
Entanglement of quantum variables is usually thought to be a prerequisite for
obtaining quantum speed-ups of information processing tasks such as searching
databases. This paper presents methods for quantum search that give a speed-up
over classical methods, but that do not require entanglement. These methods
rely instead on interference to provide a speed-up. Search without entanglement
comes at a cost: although they outperform analogous classical devices, the
quantum devices that perform the search are not universal quantum computers and
require exponentially greater overhead than a quantum computer that operates
using entanglement. Quantum search without entanglement is compared to
classical search using waves.Comment: 9 pages, TeX, submitted to Physical Review Letter
Effect of work:rest ratio on cycling performance following sprint interval training: A randomised control trial
Sprint interval training (SIT) has been shown to improve performance measures in a range of individuals, and it is understood that different responses can be elicited from different training protocols. However, consideration of changes in work: rest ratios could offer important insight into optimising training programmes. The purpose of this study was to investigate the effect of three different work: rest ratios on exercise performance. Thirty-six male and female participants were randomly allocated to one of three training groups, or a non-training control group. Training consisted of 10x6 second âall-outâ sprints on a cycle ergometer, with a 1:8, 1:10 or 1:12 work: rest ratio. Performance data, including peak power output, performance decrement, and 10km time trial performance data were collected before and after 2-weeks of SIT. There were significant (p †0.05) improvements in all parameters for the training groups, but no changes in the control condition. Peak power increased by 57.2W, 50.7W and 53.7W in the 1:8, 1:10 and 1:12 groups respectively, with no significant differences in response between conditions. Time trial performance improved significantly in all three training conditions (29.4s, 8.7s, and 25.1s in the 1:8, 1:10 and 1:12 groups), while worsening in the control group. All training conditions resulted in significant improvements in performance, but there were no significant differences in improvement for any of the groups. Any of the three stated work: rest ratios would be appropriate for use with athletes and allow some level of personal preference for those interested in using the protocol
Crossing the Brown Dwarf Desert Using Adaptive Optics: A Very Close L-Dwarf Companion to the Nearby Solar Analog HR 7672
We have found a very faint companion to the active solar analog HR 7672 (HD
190406; GJ 779; 15 Sge). Three epochs of high resolution imaging using adaptive
optics (AO) at the Gemini-North and Keck II Telescopes demonstrate that HR
7672B is a common proper motion companion, with a separation of 0.79" (14 AU)
and a 2.16 um flux ratio of 8.6 mags. Using follow-up K-band spectroscopy from
Keck AO+NIRSPEC, we measure a spectral type of L4.5+/-1.5. This is the closest
ultracool companion around a main sequence star found to date by direct
imaging. We estimate the primary has an age of 1-3 Gyr. Assuming coevality, the
companion is most likely substellar, with a mass of 55-78 Mjup based on
theoretical models. The primary star shows a long-term radial velocity trend,
and we combine the radial velocity data and AO imaging to set a firm
(model-independent) lower limit of 48 Mjup. In contrast to the paucity of brown
dwarf companions at <~4 AU around FGK dwarfs, HR 7672B implies that brown dwarf
companions do exist at separations comparable to those of the giant planets in
our own solar system. Its presence is at variance with scenarios where brown
dwarfs form as ejected stellar embryos. Moreover, since HR 7672B is likely too
massive to have formed in a circumstellar disk as planets are believed to, its
discovery suggests that a diversity of physical processes act to populate the
outer regions of exoplanetary systems.Comment: Astrophysical Journal, in pres
Implementation of a Deutsch-like quantum algorithm utilizing entanglement at the two-qubit level, on an NMR quantum information processor
We describe the experimental implementation of a recently proposed quantum
algorithm involving quantum entanglement at the level of two qubits using NMR.
The algorithm solves a generalisation of the Deutsch problem and distinguishes
between even and odd functions using fewer function calls than is possible
classically. The manipulation of entangled states of the two qubits is
essential here, unlike the Deutsch-Jozsa algorithm and the Grover's search
algorithm for two bits.Comment: 4 pages, two eps figure
Investigating geographical variation in the use of mental health services by area of England: a cross-sectional ecological study
BACKGROUND:
There is evidence of geographical variation in the use of mental health services in the UK and in international settings. It is important to understand whether this variation reflects differences in the prevalence of mental disorders, or if there is evidence of variation related to other factors, such as population socioeconomic status and access to primary care services.
METHODS:
This is a cross-sectional ecological study using Public Health England data. The unit of analysis was the population served by clinical commissioning groups (CCGs), National Health Service (NHS) catchment areas. The analysis explored associations between area characteristics and the number of people in contact with mental health services using regression modelling. Explanatory variables included age, gender, prevalence of severe mental illness (SMI), prevalence of common mental disorder (CMD), index of multiple deprivation (IMD), unemployment, proportion of the population who are Black and Minority Ethnic (BAME), population density, access to and recovery in primary care psychological therapies. Unadjusted results are reported, as well as estimates adjusted for age, prevalence of CMD and prevalence of SMI.
RESULTS:
The populations of 194 CCGs were included, clustered within 62 trusts (NHS providers of mental health services). The number of people in contact with mental health services showed wide variation by area (range from 1131 to 5205 per 100,000 population). Unemployment (adjusted IRR 1.11; 95% CI 1.05 to 1.17; pâ<â0.001) and deprivation (adjusted IRR 1.02 95% CI 1.01 to 1.04; pâ<â0.001) were associated with more people being in contact with mental health services. Areas with a higher proportion of the population who are BAME (IRR 0.95 95% CI 0.92 to 0.99 pâ=â0.007) had lower service use per 100,000 population. There was no evidence for association with access to primary care psychological therapies.
CONCLUSIONS:
There is substantial variation in the use of mental health services by area of England. Social factors including deprivation, unemployment and population ethnicity continued to be associated with the outcome after controlling for the prevalence of mental illness. This suggests that there are factors that influence the local population use of mental health services in addition to the prevalence of mental disorder
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