359 research outputs found
Analysis of the operation of gradient echo memories using a quantum input-output model
The gradient echo memory (GEM) technique is a promising candidate for real devices due to its demonstrated performance, but to date high performance experiments can only be described numerically. In this paper we derive a model for GEM as a cascade of in
Optimising the Efficiency of a Quantum Memory based on Rephased Amplified Spontaneous Emission
We studied the recall efficiency as a function of optical depth of rephased
amplified spontaneous emission (RASE), a protocol for generating entangled
light. The experiments were performed on the
transition in the rare-earth doped crystal
Pr:YSiO, using a four-level echo sequence between four
hyperfine levels to rephase the emission. Rephased emission was observed for
optical depths in the range of = 0.8 to 2.0 with a maximum rephasing
efficiency of 14 % observed while incorporating spin storage. This efficiency
is a significant improvement over the previously reported non-classical result
but is well short of the predicted efficiency. We discuss the possible
mechanisms limiting the protocol's performance, and suggest ways to overcome
these limits.Comment: 5 pages, 5 figure
NV--N+ pair centre in 1b diamond
With the creation of nitrogen (NV) in 1b diamond it is common to find that the absorption and emission is predominantly of negatively charged NV centres. This occurs because electrons tunnel from the substitutional nitrogen atoms to NV to form NV−–N+ pairs. There can be a small percentage of neutral charge NV0 centres and a linear increase of this percentage can be obtained with optical intensity. Subsequent to excitation it is found that the line width of the NV− zero-phonon has been altered. The alteration arises from a change of the distribution of N+ ions and a modification of the average electric field at the NV− sites. The consequence is a change to the Stark shifts and splittings giving the change of the zero-phonon line (ZPL) width. Exciting the NV− centres enhances the density of close N+ ions and there is a broadening of the ZPL. Alternatively exciting and ionizing N0 in the lattice results in more distant distribution of N+ ions and a narrowing of the ZPL. The competition between NV− and N0 excitation results in a significant dependence on excitation wavelength and there is also a dependence on the concentration of the NV− and N0 in the samples. The present investigation involves extensive use of low temperature optical spectroscopy to monitor changes to the absorption and emission spectra particularly the widths of the ZPL. The studies lead to a good understanding of the properties of the NV−–N+ pairs in diamond. There is a critical dependence on pair separation. When the NV−–N+ pair separation is large the properties are as for single sites and a high degree of optically induced spin polarization is attainable. When the separation decreases the emission is reduced, the lifetime shortened and the spin polarization downgraded. With separations of <12 A0 there is even no emission. The deterioration occurs as a consequence of electron tunneling in the excited state from NV– to N+ and an optical cycle that involves NV0. The number of pairs with the smaller separations and poorer properties will increase with the number of nitrogen impurities and it follows that the degree of spin polarization that can be achieved for an ensemble of NV− in 1b diamond will be determined and limited by the concentration of single substitutional nitrogen. The information will be invaluable for obtaining optimal conditions when ensembles of NV− are required. As well as extensive measurements of the NV− optical ZPL observations of Stark effects associated with the infrared line at 1042 nm and the optically detected magnetic resonance at 2.87 GHz are also reported
TranspoGene and microTranspoGene: transposed elements influence on the transcriptome of seven vertebrates and invertebrates
Transposed elements (TEs) are mobile genetic sequences. During the evolution
of eukaryotes TEs were inserted into active protein-coding genes, affecting
gene structure, expression and splicing patterns, and protein sequences.
Genomic insertions of TEs also led to creation and expression of new functional
non-coding RNAs such as micro- RNAs. We have constructed the TranspoGene
database, which covers TEs located inside proteincoding genes of seven species:
human, mouse, chicken, zebrafish, fruit fly, nematode and sea squirt. TEs were
classified according to location within the gene: proximal promoter TEs,
exonized TEs (insertion within an intron that led to exon creation), exonic TEs
(insertion into an existing exon) or intronic TEs. TranspoGene contains
information regarding specific type and family of the TEs, genomic and mRNA
location, sequence, supporting transcript accession and alignment to the TE
consensus sequence. The database also contains host gene specific data: gene
name, genomic location, Swiss-Prot and RefSeq accessions, diseases associated
with the gene and splicing pattern. In addition, we created microTranspoGene: a
database of human, mouse, zebrafish and nematode TEderived microRNAs. The
TranspoGene and micro- TranspoGene databases can be used by researchers
interested in the effect of TE insertion on the eukaryotic transcriptome
PD-1 suppresses the maintenance of cell couples between cytotoxic T cells and tumor target cells within the tumor
Assessing the feasibility of density estimation methodologies for African forest elephant at large spatial scales:estimating density of forest elephants using spatial capture-recapture
Effective wildlife management requires information on population status and distribution. Survey methods that provide estimates of these population parameters can vary greatly in effort required, area covered, precision of estimates, and cost. Trade-offs are required, because increasing precision and area coverage generally requires increasing field effort and incurs a higher cost. We compare DNA- and camera trap based-spatial capture-recapture approaches (DNA-SCR and CT-SCR) to the widely-used, dung-based line transect distance sampling (LTDS) method to assess their performance when applied to three relatively large populations of forest elephant Loxodonta cyclotis (>500 individuals), in order to evaluate their feasibility for future use at national and regional scales. Six of the nine surveys had a coefficient of variation below 20%; area coverage via DNA-SCR and LTDS was comparable and greatly exceeded that of the CT-SCR as applied; overall cost was highest for the LTDS surveys compared to the other two methods. We designed a new metric with which to compare survey methods: an integrated feasibility index (IFI). This combines three typical survey components: total area covered, level of precision achieved, and cost. The IFI suggests that DNA-SCR and LTDS are equally acceptable in terms of the combination of the three survey components, and that either survey method is suitable for large (national or regional) spatial scales for forest elephant density estimation. CT-SCR provides more precise estimates, but has double the IFI, due to the high cost per km2. DNA-SCR in particular, given the improvements highlighted in this study, is now being used at a national scale in Gabon. In conclusion, we recommend that the use of these spatial capture-recapture (SCR) methods, and their development, continue. Future findings and improvements should be compiled across studies to ensure their robust evolution as an option for monitoring the African forest elephant across its range and inform strategies and action for its conservation
The Effectiveness of Medical Simulation in Teaching Medical Students Critical Care Medicine: A Systematic Review and Meta-analysis
We aimed to assess effectiveness of simulation for teaching medical students critical care medicine and to assess which simulation methods were most useful. We searched AMED, EMBASE, MEDLINE, ERIC, BEI, AEI, plus bibliographies and
citations, to July 2013. Randomised controlled trials comparing effectiveness of simulation with another educational intervention, or no teaching, for teaching medical students critical care medicine were included. Assessments for inclusion, quality and data extraction were duplicated and results synthesised using meta-analysis.
We included 22 RCTs (n=1325). Fifteen studies comparing simulation with other teaching found simulation to be more effective (SMD 0.84, 95% CI 0.43 to 1.24; p<0.001; I2 89%). High-fidelity simulation was more effective than low-fidelity and subgrouping supported high-fidelity simulation being more effective than other methods. Simulation improved skill acquisition (SMD 1.01, 95% CI 0.49 to 1.53) but was no better than other teaching in knowledge acquisition (SMD 0.41, 95% CI -0.09 to 0.91)
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