1,415 research outputs found
Optical properties of coupled metal-semiconductor and metal-molecule nanocrystal complexes: the role of multipole effects
We investigate theoretically the effects of interaction between an optical
dipole (semiconductor quantum dot or molecule) and metal nanoparticles. The
calculated absorption spectra of hybrid structures demonstrate strong effects
of interference coming from the exciton-plasmon coupling. In particular, the
absorption spectra acquire characteristic asymmetric lineshapes and strong
anti-resonances. We present here an exact solution of the problem beyond the
dipole approximation and find that the multipole treatment of the interaction
is crucial for the understanding of strongly-interacting exciton-plasmon
nano-systems. Interestingly, the visibility of the exciton resonance becomes
greatly enhanced for small inter-particle distances due to the interference
phenomenon, multipole effects, and electromagnetic enhancement. We find that
the destructive interference is particularly strong. Using our exact theory, we
show that the interference effects can be observed experimentally even in the
exciting systems at room temperature.Comment: 9 page
Tracing the evolutionary stage of Bok globules: CCS and NH3
We pursue the investigation of a previously proposed correlation between
chemical properties and physical evolutionary stage of isolated low-mass
star-forming regions. In the past, the NH3/CCS abundance ratio was suggested to
be a potentially useful indicator for the evolutionary stage of cloud cores. We
aim to study its applicability for isolated Bok globules. A sample of 42 Bok
globules with and without signs of current star formation was searched for
CCS(2-1) emission, the observations were complemented with NH3 measurements
available in the literature and own observations. The abundance ratio of both
molecules is discussed with respect to the evolutionary stage of the objects
and in the context of chemical models. The NH3/CCS ratio could be assessed for
18 Bok globules and is found to be moderately high and roughly similar across
all evolutionary stages from starless and prestellar cores towards internally
heated cores harbouring protostars of Class 0, Class I or later. Bok globules
with extremely high CCS abundance analogous to carbon-chain producing regions
in dark cloud cores are not found. The observed range of NH3/CCS hints towards
a relatively evolved chemical state of all observed Bok globules.Comment: 12 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
On a universal photonic tunnelling time
We consider photonic tunnelling through evanescent regions and obtain general
analytic expressions for the transit (phase) time (in the opaque barrier
limit) in order to study the recently proposed ``universality'' property
according to which is given by the reciprocal of the photon frequency.
We consider different physical phenomena (corresponding to performed
experiments) and show that such a property is only an approximation. In
particular we find that the ``correction'' factor is a constant term for total
internal reflection and quarter-wave photonic bandgap, while it is
frequency-dependent in the case of undersized waveguide and distributed Bragg
reflector. The comparison of our predictions with the experimental results
shows quite a good agreement with observations and reveals the range of
applicability of the approximated ``universality'' property.Comment: RevTeX, 8 pages, 4 figures, 1 table; subsection added with a new
experiment analyzed, some other minor change
Metals in Particulate Pollutants Affect Peak Expiratory Flow of Schoolchildren
BACKGROUND: The contribution of the metal components of particulate pollutants to acute respiratory effects has not been adequately evaluated. Moreover, little is known about the effects of genetic polymorphisms of xenobiotic metabolism on pulmonary function. OBJECTIVES: This study was conducted to assess lung function decrement associated with metal components in particulate pollutants and genetic polymorphisms of glutathione S-transferase M1 and T1. METHODS: We studied 43 schoolchildren who were in the 3rd to 6th grades. Each student measured peak expiratory flow rate three times a day for 42 days. Particulate air concentrations were monitored every day, and the concentrations of iron, manganese, lead, zinc, and aluminum in the particles were measured. Glutathione S-transferase M1 and T1 genetic polymorphisms were determined using DNA extracted from participant buccal washings. We used a mixed linear regression model to estimate the association between peak expiratory flow rate and particulate air pollutants. RESULTS: We found significant reduction in the peak expiratory flow rate after the children’s exposure to particulate pollutants. The effect was shown most significantly 1 day after exposure to the ambient particles. Manganese and lead in the particles also reduced the peak expiratory flow rate. Genetic polymorphisms of glutathione S-transferase M1 and T1 did not significantly affect peak expiratory flow rate. CONCLUSIONS: This study demonstrated that particulate pollutants and metals such as manganese and lead in the particles are associated with a decrement of peak expiratory flow rate. These effects were robust even with consideration of genetic polymorphisms of glutathione S-transferase
Looking into the hearts of Bok globules: MM and submm continuum images of isolated star-forming cores
We present the results of a comprehensive infrared, submillimetre, and
millimetre continuum emission study of isolated low-mass star-forming cores in
32 Bok globules, with the aim to investigate the process of star formation in
these regions. The submillimetre and millimetre dust continuum emission maps
together with the spectral energy distributions are used to model and derive
the physical properties of the star-forming cores, such as luminosities, sizes,
masses, densities, etc. Comparisons with ground-based near-infrared and
space-based mid and far-infrared images from Spitzer are used to reveal the
stellar content of the Bok globules, association of embedded young stellar
objects with the submm dust cores, and the evolutionary stages of the
individual sources. Submm dust continuum emission was detected in 26 out of the
32 globule cores observed. For 18 globules with detected (sub)mm cores we
derive evolutionary stages and physical parameters of the embedded sources. We
identify nine starless cores, most of which are presumably prestellar, nine
Class 0 protostars, and twelve Class I YSOs. Specific source properties like
bolometric temperature, core size, and central densities are discussed as
function of evolutionary stage. We find that at least two thirds (16 out of 24)
of the star-forming globules studied here show evidence of forming multiple
stars on scales between 1,000 and 50,000 AU. However, we also find that most of
these small prototstar and star groups are comprised of sources with different
evolutionary stages, suggesting a picture of slow and sequential star formation
in isolated globulesComment: 60 pages, 28 figures, accepted by The Astrophysical Journal
Supplement Serie
DNA resection in eukaryotes: deciding how to fix the break
DNA double-strand breaks are repaired by different mechanisms, including homologous
recombination and nonhomologous end-joining. DNA-end resection, the first step in
recombination, is a key step that contributes to the choice of DSB repair. Resection, an
evolutionarily conserved process that generates single-stranded DNA, is linked to checkpoint
activation and is critical for survival. Failure to regulate and execute this process results in
defective recombination and can contribute to human disease. Here, I review recent findings on
the mechanisms of resection in eukaryotes, from yeast to vertebrates, provide insights into the
regulatory strategies that control it, and highlight the consequences of both its impairment and its
deregulation
Therapeutic foam scaffolds incorporating biopolymer-shelled mesoporous nanospheres with growth factors
Here we report a novel therapeutic scaffolding system of engineered nanocarriers within a foam matrix for the long-term and sequential delivery of growth factors. For this, mesoporous silica nanospheres were first functionalized to have enlarged mesopore size (eMSNs, 12.2 nm) and aminated surface, which was then shelled by a biopolymer, poly(lactic acid) (PLA) or poly(ethylene glycol) (PEG) via an electrospraying. The hybrid nanocarrier was subsequently combined with collagen to produce foam scaffolds. Bovine serum albumin (BSA), used as a model protein, was effectively loaded within the enlarged nanospheres. The biopolymer shell substantially prolonged the release period of BSA (over 2-3 weeks from shelled nanospheres vs. within 1 week from bare nanospheres), and the release rate was highly dependent on the shell composition (PEG > PLA). Collagen foam scaffolding of the shelled nanocarrier further slowed down the protein release while enabling the incorporation of a rapidly releasing protein, which is effective for the sequential protein delivery. Acidic fibroblast growth factor (aFGF), loaded onto the shelled-nanocarrier scaffolds, was released over a month at a highly sustainable rate, profiling a similar release pattern to BSA. Biological activity of the aFGF released from the system, as examined by the proliferative potential of osteoblastic precursor cells, showed a significant improvement in the case with aFGF. Furthermore, in vivo implantation of the aFGF-delivering system in a rat subcutaneous tissue for 2 weeks showed a substantially enhanced invasion of fibroblasts with a homogeneous population. Taken together, it is concluded that the biopolymer encapsulation of mesoporous nanospheres effectively prolongs the release of growth factors over weeks to a month, providing a nanocarrier platform for a long-term growth factor delivery, moreover, the foam scaffolding of the nanocarrier system will be a potential therapeutic 3D matrix for cell culture and tissue engineering
Distribution of Introns in Fungal Histone Genes
Saccharomycotina and Taphrinomycotina lack intron in their histone genes, except for an intron in one of histone H4 genes of Yarrowia lipolytica. On the other hand, Basidiomycota and Perizomycotina have introns in their histone genes. We compared the distributions of 81, 47, 79, and 98 introns in the fungal histone H2A, H2B, H3, and H4 genes, respectively. Based on the multiple alignments of the amino acid sequences of histones, we identified 19, 13, 31, and 22 intron insertion sites in the histone H2A, H2B, H3, and H4 genes, respectively. Surprisingly only one hot spot of introns in the histone H2A gene is shared between Basidiomycota and Perizomycotina, suggesting that most of introns of Basidiomycota and Perizomycotina were acquired independently. Our findings suggest that the common ancestor of Ascomycota and Basidiomycota maybe had a few introns in the histone genes. In the course of fungal evolution, Saccharomycotina and Taphrinomycotina lost the histone introns; Basidiomycota and Perizomycotina acquired other introns independently. In addition, most of the introns have sequence similarity among introns of phylogenetically close species, strongly suggesting that horizontal intron transfer events between phylogenetically distant species have not occurred recently in the fungal histone genes
Clinical and laboratory findings associated with severe scrub typhus
<p>Abstract</p> <p>Background</p> <p>Scrub typhus is a mite-borne bacterial infection of humans caused by <it>Orientia tsutsugamushi </it>that causes a generalized vasculitis that may involve the tissues of any organ system. The aim of this study was to identify factors associated to severe complications from scrub typhus.</p> <p>Methods</p> <p>We conducted this prospective, case-control study on scrub typhus patients who presented to the Department of Internal Medicine at Chosun University Hospital between September, 2004 and December, 2006. Cases were 89 scrub typhus patients with severe complications and controls were 119 scrub typhus patients without severe complications.</p> <p>Results</p> <p>There were significant differences in the absence of eschar, white blood cell (WBC) counts, hemoglobin, albumin, serum creatinine, fibrinogen, C-reactive protein (CRP), and active partial thromboplastin time (aPTT) between the two groups. Multivariate analysis demonstrated that only the following four factors were significantly associated with the severe complications of scrub typhus: (1) age ≥ 60 years (odd ratio [OR] = 3.13, <it>P </it>= 0.002, confidence interval [CI] = 1.53-6.41), (2) the absence of eschar (OR = 6.62, <it>P </it>= 0.03, CI = 1.22-35.8, (3) WBC counts > 10, 000/mm3 (OR = 3.6, <it>P </it>= 0.001, CI = 1.65-7.89), and (4) albumin ≤ 3.0 g/dL (OR = 5.01, <it>P </it>= 0.004, CI = 1.69-14.86).</p> <p>Conclusions</p> <p>Our results suggest that clinicians should be aware of the potential for complications, when scrub typhus patients are older (≥ 60 years), presents without eschar, or laboratory findings such as WBC counts > 10, 000/mm3, and serum albumin level ≤ 3.0 g/dL. Close observation and intensive care for scrub typhus patients with the potential for complications may prevent serious complications with subsequent reduction in its mortality rate.</p
The generalized Hamiltonian model for the shafting transient analysis of the hydro turbine generating sets.
yesTraditional rotor dynamics mainly focuses on the steady- state behavior of the rotor and shafting. However, for systems such as hydro turbine generating sets (HTGS) where the control and regulation is frequently applied, the shafting safety and stabilization in transient state is then a key factor. The shafting transient state inevitably involves multiparameter domain, multifield coupling, and coupling dynamics. In this paper, the relative value form of the Lagrange function and its equations have been established by defining the base value system of the shafting. Takingthe rotation angle and the angular speed of the shafting as a link, the shafting lateral vibration and generator equations are integrated into the framework of generalized
Hamiltonian system. The generalized Hamiltonian control model is thus established. To make the model more general, additional forces of the shafting are taken as the input excitation in proposed model. The control system of the HTGS can be easily connected with the shafting model to form the whole simulation system of the HTGS. It is expected that this study will
build a foundation for the coupling dynamics theory using the generalized Hamiltonian theory to investigate coupling dynamic mechanism among the shafting vibration, transient of hydro turbine generating sets, and additional forces of the shafting.National Natural Science Foundation of China under Grant Nos. 51179079 and 5083900
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