1,428 research outputs found
High-repetition-rate combustion thermometry with two-line atomic fluorescence excited by diode lasers
We report on kilohertz-repetition-rate flame temperature measurements performed using blue diode lasers. Two-line atomic fluorescence was performed by using diode lasers emitting at around 410 and 451 nm to probe seeded atomic indium. At a repetition rate of 3.5 kHz our technique offers a precision of 1.5% at 2000 K in laminar methane/air flames. The spatial resolution is better than 150 mu m, while the setup is compact and easy to operate, at much lower cost than alternative techniques. By modeling the spectral overlap between the locked laser and the probed indium lines we avoid the need for any calibration of the measurements. We demonstrate the capability of the technique for time-resolved measurements in an acoustically perturbed flame. The technique is applicable in flames with a wide range of compositions including sooting flames
Nonlinear optical properties of a channel waveguide produced with crosslinkable ferroelectric liquid crystals
A binary mixture of ferroelectric liquid crystals (FLCs) was used for the
design of a channel waveguide. The FLCs possess two important functionalities:
a chromophore with a high hyperpolarizability and photoreactive groups.
The smectic liquid crystal is aligned in layers parallel to the glass plates in
a sandwich geometry. This alignment offers several advantages, such as that
moderate electric fields are sufficient to achieve a high degree of polar
order. The arrangement was then permanently fixed by photopolymerization which
yielded a polar network possessing a high thermal and mechanical stability
which did not show any sign of degradation within the monitored period of
several months. The linear and nonlinear optical properties have been measured
and all four independent components of the nonlinear susceptibility tensor
have been determined. The off-resonant -coefficients are remarkably
high and comparable to those of the best known inorganic materials. The
alignment led to an inherent channel waveguide for p-polarized light without
additional preparation steps. The photopolymerization did not induce scattering
sites in the waveguide and the normalized losses were less than 2 dB/cm. The
material offers a great potential for the design of nonlinear optical devices
such as frequency doublers of low power laser diodes.Comment: LaTeX2e article, 15 pages, 10 figures, 11 EPS files, submitted to
Physical Review
Phase-matched second-harmonic generation in a ferroelectric liquid crystal waveguide
True phase-matched second-harmonic generation in a waveguide of crosslinkable
ferroelectric liquid crystals is demonstrated. These materials allow the
formation of macroscopically polar structures whose order can be frozen by
photopolymerization. Homeotropic alignment was chosen which offers decisive
advantages compared to other geometries. All parameters contributing to the
conversion efficiency are maximized by deliberately controlling the
supramolecular arrangement. The system has the potential to achieve practical
level of performances as a frequency doubler for low power laser diodes.Comment: 4 pages, LaTeX2e article, 3 figures, 4 EPS files, submitted to
Physical Review Letter
Flow cytometric evaluation of red blood cells transformed with variable amounts of synthetic A and B glycolipids
Background: According to national guidelines or directives, monoclonal
ABO reagents may be required to detect Ax and B weak subgroup red blood
cells (RBCs). Many routine laboratories do not have access to naturallyoccurring
ABO subgroups that can be used as weak controls for these
reagents. Group O RBCs modified with synthetic analogs of blood group A
and/or B glycolipids (KODE technology) to mimic weak ABO subgroups
could be used for quality control purposes.
Aim: Extensive serological testing of KODE RBCs has previously been
performed. An extended evaluation of KODE RBCs using flow cytometry
was performed to explore the correlation between the concentrations of
synthetic glycolipids and A/B site density of the resulting RBCs. The aim of
this study was to examine if KODE RBCs mimic the distinct flow cytometric
patterns of naturally-occurring ABO subgroups.
Material and Methods: KODE RBCs were prepared according to a previously
decribed procedure [Frame et al., Transfusion 2007; 47: 876–82].
RBCs were modified with 15 different concentrations of synthetic glycolipids,
ranging from 1 mg/mL to 60 ng/mL for KODE-A and 5 mg/mL to
0.3 lg/mL for KODE-B. The concentration was decreased by doubling
dilution steps. Sensitive and specific flow cytometry [Hult & Olsson.
Transfusion 2006; 9S: 32A] was used to characterize and semiquantify the
synthetic A and B antigen levels on RBCs. Relevant control RBCs (A1, A2,
Ax, B, Bweak and O) were included in each run. For both KODE-A and KODE-B RBCs, repeat samples were produced for four selected concentrations
and all KODE batches were tested in triplicate.
Results: Flow cytometric testing of KODE RBCs modified with high
concentrations of synthetic glycolipids revealed a uniform and even
distribution of antigens in the cell population as shown by a single
narrow peak in the FACS histograms. When lower concentrations were
used, peaks tended to broaden to a pattern found in Ax and most B
subgroups indicating a more variable antigen site density on the cells in
the population. The concentrations of synthetic glycolipids that produced
KODE cells that resembled the naturally-occurring subgroup control RBCs
used in this study are ~2–4 lg/mL for KODE-A and ~10 lg/mL for KODEB.
Repeat testing demonstrated good correlation between flow cytometric
runs.
Discussion and Conclusion: Using very low amounts of synthetic
glycolipids, KODE-A and KODE-B RBCs can be made to mimic Ax and
Bweak subgroup control RBCs, respectively, according to this flow
cytometry method. With higher concentrations of synthetic glycolipids, the
KODE RBCs demonstrated a more uniform and even distribution of antigens
among the cells. This is in contrast to naturally-occurring subgroups
in which some cells express almost no A or B antigen whilst others have
close to normal levels. The reason for this is unknown. KODE RBCs obviously
lack A carrying glycoproteins but it is not fully understood to what
extent glycolipid versus glycoprotein epitopes contribute to the phenotype
of weak subgroups.
This study indicates that KODE RBCs with weak expression of A and/or B
antigen have characteristics compatible with use as quality controls for
monoclonal ABO reagents and could be a valuable addition in the
serological laboratory
On the Underground Production of High Purity Germanium Detectors
Detectors based on high purity germanium (HPGe) are used in numerous deep underground experiments world-wide aiming at detecting rare events like double beta decay and interactions of dark matter. These detectors require the lowest possible background. A significant part of the background is due to radionuclides produced by cosmic-ray interactions with the germanium crystal. This report gives quantitative data on this activation and discusses the possible solutions. The first solution is to optimise the logistics during the crystal and detector fabrication so that the germanium spends a minimum time above ground. The second solution is to implement one or several (up to 12) production steps underground. The report also makes estimates on the future needs for germanium produced underground and the costs involved.JRC.D.4-Isotope measurement
Revisiting the firm, industry, and country effects on profitability under recessionary and expansion periods: a multilevel analysis
Despite voluminous past research, the relevance of firm, industry, and country effects on profitability, particularly under adverse contexts, is still unclear. We reconcile institutional theory with the resource‐based view and industrial organization economics to investigate the effects of economic adversity, such as the 2008 global economic crisis. Using a three‐level random coefficient model, we examine 15,008 firms across 10 emerging and 10 developed countries for the 2005–2011 period. We find that firm effects become stronger under adversity, whereas industry effects become weaker, as well as country main and interaction effects, particularly among the emerging economies. These findings confirm our assumptions that the firm's own fate is, to a great extent, self‐determined; a reality that is even more pronounced during periods of extreme economic hardship
Low-Background gamma counting at the Kimballton Underground Research Facility
The next generation of low-background physics experiments will require the
use of materials with unprecedented radio-purity. A gamma-counting facility at
the Kimballton Underground Research Facility (KURF) has been commissioned to
perform initial screening of materials for radioactivity primarily from
nuclides in the 238U and 232Th decay chains, 40K and cosmic-ray induced
isotopes. The facility consists of two commercial low-background high purity
germanium (HPGe) detectors. A continuum background reduction better than a
factor of 10 was achieved by going underground. This paper describes the
facility, detector systems, analysis techniques and selected assay results.Comment: 7 pages, 7 figures. Submitted to NIM
Highly sensitive gamma-spectrometers of GERDA for material screening: Part I
The GERDA experiment aims to search for the neutrinoless double beta-decay of
76Ge and possibly for other rare processes. The sensitivity of the first phase
is envisioned to be more than one order of magnitude better than in previous
neutrinoless double beta-decay experiments. This implies that materials with
ultra-low radioactive contamination need to be used for the construction of the
detector and its shielding. Therefore the requirements on material screening
include high-sensitivity low-background detection techniques and long
measurement times. In this article, an overview of material-screening
laboratories available to the GERDA collaboration is given, with emphasis on
the gamma-spectrometry. Additionally, results of an intercomparison of the
evaluation accuracy in these laboratories are presented.Comment: Featured in: Proceedings of the XIV International Baksan School
"Particles and Cosmology" Baksan Valley, Kabardino-Balkaria, Russia, April
16-21,2007. INR RAS, Moscow 2008. ISBN 978-5-94274-055-9, pp. 228-232; (5
pages, 0 figures
Dicarboxylic esters : useful tools for the biocatalyzed synthesis of hybrid compounds and polymers
Dicarboxylic acids and their derivatives (esters and anhydrides) have been used as acylating agents in lipase-catalyzed reactions in organic solvents. The synthetic outcomes have been dimeric or hybrid derivatives of bioactive natural compounds as well as functionalized polyesters
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