330 research outputs found
Advanced Photodetectors for Hyperspectroscopy and Other Applications
Hyperspectroscopy is a new method of surface image taking, providing
simultaneously high position and spectral resolutions which allow one to make
some conclusions about chemical compositions of the surfaces. We are now
studying applications of the hyperspctroscopic technique to be used for
medicine. This may allow one to develop early diagnostics of some illnesses, as
for example, skin cancer. For image taking advanced MCPs are currently used,
sensitive in the spectral interval of 450-850 nm. One of the aims of this work
is to extend the hyperspectrocpic method to the UV region of spectra: 185-280
nm. For this we have developed and successfully tested innovative 1D and 2D UV
sealed photosensitive gaseous detectors with resistive electrodes. These
detectors are superior MCPs due to the very low rate of noise pulses and thus
due to the high signal to noise ratio. Other important features of these
detectors are that they have excellent position resolutions - 30 micron in
digital form, are vibration stable and are spark protected. The first results
from the application of these detectors for spectroscopy, hyperspectroscopy and
the flame detection are presented.Comment: Presented at the IEEE Nuclear Science Syposium, Puerto Rico, October
200
The first applications of novel gaseous detectors for UV visualization
We have demonstrated experimentally that recently developed gaseous detectors combined with solid or gaseous photo-cathodes have exceptionally low noise and high quantum efficiency for UV photons while being solar blind. For this reason they can be used for the detection of weak UV sources in daylight conditions. These detectors are extremely robust, can operate in poor gas conditions and are cheap. We present the first results of their applications to hyper-spectroscopy and flame detection in daylight conditions
Weak ferromagnetism and field-induced spin reorientation in K2V3O8
Magnetization and neutron diffraction measurements indicate long-range
antiferromagnetic ordering below TN=4 K in the 2D, S=1/2 Heisenberg
antiferromagnet K2V3O8. The ordered state exhibits ``weak ferromagnetism'' and
novel, field-induced spin reorientations. These experimental observations are
well described by a classical, two-spin Heisenberg model incorporating
Dzyaloshinskii-Moriya interactions and an additional c-axis anisotropy. This
additional anisotropy can be accounted for by inclusion of the symmetric
anisotropy term recently described by Kaplan, Shekhtman, Entin-Wohlman, and
Aharony. This suggests that K2V3O8 may be a very unique system where the
qualitative behavior relies on the presence of this symmetric anisotropy.Comment: 5 pages, 4 ps figures, REVTEX, submitted to PR
Modeling the electronic behavior of -LiV2O5: a microscopic study
We determine the electronic structure of the one-dimensional spin-1/2
Heisenberg compound -LiVO, which has two inequivalent vanadium
ions, V(1) and V(2), via density-functional calculations. We find a relative
V(1)-V(2) charge ordering of roughly . We discuss the influence of the
charge ordering on the electronic structure and the magnetic behavior. We give
estimates of the basic hopping matrix elements and compare with the most
studied -NaVO.Comment: Final version. To appear in Phys. Rev. Let
Morphology of inorganic–organic systems consisting of polyhedral oligomeric silsesquioxanes (POSS) and polyamide 6
Preparation of inorganic-organic hybrids made of polyhedral oligomeric silsesquioxanes (POSS) and polyamide 6 (PA6) has been attempted either by melt mixing of the two components or by in-situ polymerization of e-caprolactam (CL) in presence of POSS. The samples have been characterized by wide angle X-ray diffraction (WAXD) and scanning electron microscopy (SEM) techniques. Specific processing conditions (namely, high T in presence of different shear stresses) have been tested. Two different approaches for melt mixing have been used and the morphology of the corresponding systems compared. The melt-mixed pairs prepared in the microcompounder revealed a coarse phase separation, while those made in a simple mixer did not show any perceivable POSS segregation phenomenon, as evidenced by both WAXD data and SEM investigation. Similarly, the in-situ polymerization of CL in presence of POSS did not result in any POSS self-aggregation in the polyamide matrix, achieving a very fine Si dispersion of nanometric dimensions
Clues for a standardised thermal-optical protocol for the assessment of organic and elemental carbon within ambient air particulate matter
Along with some research networking programmes, the European Directive
2008/50/CE requires chemical speciation of fine aerosol (PM<sub>2.5</sub>),
including elemental (EC) and organic carbon (OC), at a few rural sites in
European countries. Meanwhile, the thermal-optical technique is considered by
the European and US networking agencies and normalisation bodies as a
reference method to quantify EC–OC collected on filters. Although commonly
used for many years, this technique still suffers from a lack of
information on the comparability of the different analytical protocols
(temperature protocols, type of optical correction) currently applied in the
laboratories. To better evaluate the EC–OC data set quality and related
uncertainties, the French National Reference Laboratory for Ambient Air
Quality Monitoring (LCSQA) organised an EC–OC comparison exercise for
French laboratories using different thermal-optical methods (five laboratories
only). While there is good agreement on total carbon (TC) measurements among
all participants, some differences can be observed on the EC / TC ratio, even
among laboratories using the same thermal protocol. These results led to
further tests on the influence of the optical correction: results obtained
from different European laboratories confirmed that there were higher
differences between OC<sub>TOT</sub> and OC<sub>TOR</sub> measured with
NIOSH 5040 in comparison to EUSAAR-2. Also, striking differences between
EC<sub>TOT</sub> / EC<sub>TOR</sub> ratios can be observed when comparing
results obtained for rural and urban samples, with EC<sub>TOT</sub> being
50% lower than EC<sub>TOR</sub> at rural sites whereas it is only
20% lower at urban sites. The PM chemical composition could explain
these differences but the way it influences the EC–OC measurement is not
clear and needs further investigation. Meanwhile, some additional tests seem
to indicate an influence of oven soiling on the EC–OC measurement data
quality. This highlights the necessity to follow the laser signal decrease
with time and its impact on measurements. Nevertheless, this should be
confirmed by further experiments, involving more samples and various
instruments, to enable statistical processing. All these results provide
insights to determine the quality of EC–OC analytical methods and may
contribute to the work toward establishing method standardisation
Efficient organic carbon burial in the Bengal fan sustained by the Himalayan erosional system
Author Posting. © Nature Publishing Group, 2007. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature 450 (2007): 407-410, doi:10.1038/nature06273.Continental erosion controls atmospheric carbon dioxide levels on geological timescales
through silicate weathering, riverine transport and subsequent burial of organic carbon
in oceanic sediments. The efficiency of organic carbon deposition in sedimentary basins
is however limited by the organic carbon load capacity of the sediments and organic
carbon oxidation in continental margins. At the global scale, previous studies have
suggested that about 70 per cent of riverine organic carbon is returned to the
atmosphere, such as in the Amazon basin. Here we present a comprehensive organic
carbon budget for the Himalayan erosional system, including source rocks, river
sediments and marine sediments buried in the Bengal fan. We show that organic carbon
export is controlled by sediment properties, and that oxidative loss is negligible during
transport and deposition to the ocean. Our results indicate that 70 to 85 per cent of the
organic carbon is recent organic matter captured during transport, which serves as a
net sink for atmospheric carbon dioxide. The amount of organic carbon deposited in the
Bengal basin represents about 10 to 20 per cent of the total terrestrial organic carbon
buried in oceanic sediments. High erosion rates in the Himalayas generate high
sedimentation rates and low oxygen availability in the Bay of Bengal that sustain the
observed extreme organic carbon burial efficiency. Active orogenic systems generate
enhanced physical erosion and the resulting organic carbon burial buffers atmospheric
carbon dioxide levels, thereby exerting a negative feedback on climate over geological
timescales
Quantification of lentiviral vector copy numbers in individual hematopoietic colony-forming cells shows vector dose-dependent effects on the frequency and level of transduction
Lentiviral vectors are effective tools for gene transfer and integrate variable numbers of proviral DNA copies in variable proportions of cells. The levels of transduction of a cellular population may therefore depend upon experimental parameters affecting the frequency and/or the distribution of vector integration events in this population. Such analysis would require measuring vector copy numbers (VCN) in individual cells. To evaluate the transduction of hematopoietic progenitor cells at the single-cell level, we measured VCN in individual colony-forming cell (CFC) units, using an adapted quantitative PCR (Q-PCR) method. The feasibility, reproducibility and sensitivity of this approach were tested with characterized cell lines carrying known numbers of vector integration. The method was validated by correlating data in CFC with gene expression or with calculated values, and was found to slightly underestimate VCN. In spite of this, such Q-PCR on CFC was useful to compare transduction levels with different infection protocols and different vectors. Increasing the vector concentration and re-iterating the infection were two different strategies that improved transduction by increasing the frequency of transduced progenitor cells. Repeated infection also augmented the number of integrated copies and the magnitude of this effect seemed to depend on the vector preparation. Thus, the distribution of VCN in hematopoietic colonies may depend upon experimental conditions including features of vectors. This should be carefully evaluated in the context of ex vivo hematopoietic gene therapy studies
- …