167 research outputs found
de-Broglie Wave-Front Engineering
We propose a simple method for the deterministic generation of an arbitrary
continuous quantum state of the center-of-mass of an atom. The method's spatial
resolution gradually increases with the interaction time with no apparent
fundamental limitations. Such de-Broglie Wave-Front Engineering of the atomic
density can find applications in Atom Lithography, and we discuss possible
implementations of our scheme in atomic beam experiments.Comment: The figures' quality was improved, the text remains intact. 5 pages,
3 figures; submitted to PR
Radiation-Hard Optical Link for SLHC
We study the feasibility of fabricating an optical link for the SLHC ATLAS
silicon tracker based on the current pixel optical link architecture. The
electrical signals between the current pixel modules and the optical modules
are transmitted via micro-twisted cables. The optical signals between the
optical modules and the data acquisition system are transmitted via
radiation-hard/low-bandwidth SIMM fibres fusion spliced to
radiation-tolerant/medium-bandwidth GRIN fibres. The link has several nice
features. We have measured the bandwidths of the micro twisted-pair cables to
be ~ 1 Gb/s and the fusion spliced fibre ribbon to be ~ 2 Gb/s. We have
irradiated PIN and VCSEL arrays with 24 GeV protons and find the arrays can
operate up to the SLHC dosage. We have also demonstrated the feasibility of
fabricating a novel opto-pack for housing VCSEL and PIN arrays with BeO as the
substrate.Comment: 8th International Conference on Large Scale Applications and
Radiation Hardness of Semiconductor Detectors, Florence, Italy, 200
Implications of phosphor coating on the thermal characteristics of phosphor-converted white LEDs
The phosphor layer in phosphor-converted white
Light Emitting Diodes (pcLEDs) affects their optical and thermal
performances. This paper reports the effects of phosphor
thickness and particle concentration on the optical efficiency and
temperature rise on conformal phosphor-coated LED package. It
is observed that a thicker phosphor layer and a higher phosphor
particle concentration will increase the amount of backscattering
and back reflection of light from the phosphor layer. These light
extraction losses not only reduce the optical efficiency of the light
output but also cause heat accumulation in the phosphor layer,
leading to higher LED junction temperature. At 2700 K
correlated colour temperature (CCT), the temperature rise is
observed to increase by as much as 2.6 times as compared to its
blue emitting LED package. However, the self-heating effect can
be reduced through its die-bonding configuration. Structure
function-based thermal evaluation shows heat accumulation in
the phosphor layer and that flip-chip bonding can dissipate the
heat generated in the GaN LED and phosphor layer effectively.
Evidence in this study demonstrates that optical efficiency and
thermal resistance of pcLEDs are dependent on the CCT ratings
Gastric cancer and Helicobacter pylori: a combined analysis of 12 case control studies nested within prospective cohorts
BACKGROUND: The magnitude of the association
between Helicobacter pylori and
incidence of gastric cancer is unclear. H
pylori infection and the circulating antibody
response can be lost with development
of cancer; thus retrospective studies
are subject to bias resulting from classifi-
cation of cases as H pylori negative when
they were infected in the past.
AIMS: To combine data from all case control
studies nested within prospective
cohorts to assess more reliably the relative
risk of gastric cancer associated with H
pylori infection.To investigate variation in
relative risk by age, sex, cancer type and
subsite, and interval between blood sampling
and cancer diagnosis.
METHODS: Studies were eligible if blood
samples for H pylori serology were collected
before diagnosis of gastric cancer in
cases. Identified published studies and two
unpublished studies were included. Individual
subject data were obtained for
each. Matched odds ratios (ORs) and 95%
confidence intervals (95% CI) were calculated
for the association between H pylori
and gastric cancer.
RESULTS: Twelve studies with 1228 gastric
cancer cases were considered. The association
with H pylori was restricted to noncardia
cancers (OR 3.0; 95% CI 2.3–3.8)
and was stronger when blood samples for
H pylori serology were collected 10+ years
before cancer diagnosis (5.9; 3.4–10.3). H
pylori infection was not associated with an
altered overall risk of cardia cancer (1.0;
0.7–1.4).
CONCLUSIONS: These results suggest that
5.9 is the best estimate of the relative risk
of non-cardia cancer associated with H
pylori infection and that H pylori does not
increase the risk of cardia cancer. They
also support the idea that when H pylori
status is assessed close to cancer diagnosis,
the magnitude of the non-cardia
association may be underestimated
Study of the Radiation Hardness of VCSEL and PIN Arrays
The silicon trackers of the ATLAS experiment at LHC (CERN) use optical links for data transmission. VCSEL arrays operating at 850 nm are used to transmit optical signals while PIN arrays are used to convert the optical signals into electrical signals. We investigate the feasibility of using the devices at the Super LHC (SLHC). We irradiated VCSEL and GaAs PIN arrays from three vendors and silicon PIN arrays from one vendor. All arrays can be operated up to the SLHC dosage except the GaAs PIN arrays which have very low responsivities after irradiation and hence are probably not suitable for the SLHC application
Nanoscale waveguiding methods
While 32 nm lithography technology is on the horizon for integrated circuit (IC) fabrication, matching the pace for miniaturization with optics has been hampered by the diffraction limit. However, development of nanoscale components and guiding methods is burgeoning through advances in fabrication techniques and materials processing. As waveguiding presents the fundamental issue and cornerstone for ultra-high density photonic ICs, we examine the current state of methods in the field. Namely, plasmonic, metal slot and negative dielectric based waveguides as well as a few sub-micrometer techniques such as nanoribbons, high-index contrast and photonic crystals waveguides are investigated in terms of construction, transmission, and limitations. Furthermore, we discuss in detail quantum dot (QD) arrays as a gain-enabled and flexible means to transmit energy through straight paths and sharp bends. Modeling, fabrication and test results are provided and show that the QD waveguide may be effective as an alternate means to transfer light on sub-diffraction dimensions
SARS-CoV Antibody Prevalence in All Hong Kong Patient Contacts
A total of 1,068 asymptomatic close contacts of patients with severe acute respiratory (SARS) from the 2003 epidemic in Hong Kong were serologically tested, and 2 (0.19%) were positive for SARS coronavirus immunoglobulin G antibody. SARS rarely manifests as a subclinical infection, and at present, wild animal species are the only important natural reservoirs of the virus
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