4,613 research outputs found
The hardness-duration correlation in the two classes of gamma-ray bursts
The well-known hardness-duration correlation of gamma-ray bursts (GRBs) is
investigated with the data of the 4B catalog. We find that, while the hardness
ratio and the duration are obviously correlated for the entire set of the 4B
catalog, they are not at all correlated for the two subsets divided at the
duration of 2 seconds. However, for other subsets with comparable sizes, the
two quantities are significantly correlated. The following conclusions are then
reached: (1) the existence of two classes of GRBs is confirmed; (2) the
hardness ratio and the duration are not at all correlated for any of the two
classes; (3) different classes of GRBs have different distributions of the
hardness ratio and the duration and it is this difference that causes the
correlation between the two quantities for the entire set of the bursts.Comment: 5 pages, 1 figure, accepted for publication in PAS
Optimum spectral window for imaging of art with optical coherence tomography
Optical Coherence Tomography (OCT) has been shown to have potential for important applications in the field of art conservation and archaeology due to its ability to image subsurface microstructures non-invasively. However, its depth of penetration in painted objects is limited due to the strong scattering properties of artistsâ paints. VIS-NIR (400 nm â 2400 nm) reflectance spectra of a wide variety of paints made with historic artistsâ pigments have been measured. The best spectral window with which to use optical coherence tomography (OCT) for the imaging of subsurface structure of paintings was found to be around 2.2 ÎŒm. The same spectral window would also be most suitable for direct infrared imaging of preparatory sketches under the paint layers. The reflectance spectra from a large sample of chemically verified pigments provide information on the spectral transparency of historic artistsâ pigments/paints as well as a reference set of spectra for pigment identification. The results of the paper suggest that broadband sources at ~2 microns are highly desirable for OCT applications in art and potentially material science in general
Optical Coherence Tomography (OCT) for examination of artworks
Chapter in the book: Bastidas D., Cano E. (eds) Advanced Characterization Techniques, Diagnostic Tools and Evaluation Methods in Heritage Science. Springer, Cham, 2018, pp 49-59 , doi: 10.1007/978-3-319-75316-4, Authorsâversion after embargo periodOptical coherence tomography is a fast, non-invasive technique of structural analysis utilising near-infrared radiation. Examples of using OCT, for obtaining cross-sectional images of objects of craftsmanship and an easel painting have been shown. Issues regarding the technique of execution and destruction phenomena were resolved non-invasively. In some cases, the secondary alterations can be identified and localised within the objectâs structure which helps in authentication of the artwork
Immediate latissimus dorsi pedicle flap reconstruction following the removal of an eight kilogram giant phyllodes tumour of the breast: a case report
<p>Abstract</p> <p>Introduction</p> <p>Phyllodes tumors account for less than 1% of breast tumors in women, and giant phyllodes tumors are those that are larger than 10 cm in diameter. Removal of such large tumors places a huge burden on the surgeon to reconstruct a breast that is aesthetically acceptable by the patient. We report what may be the largest giant phyllodes tumor and, most likely, the first latissimus dorsi flap used to cover such a large defect caused by the resection.</p> <p>Case presentation</p> <p>We report the case of a 36-year-old Malaysian woman who presented with a three-year history of gradually increasing swelling of the left breast, with skin changes. Examination revealed a huge, globular, lobulated mass measuring 400 mm by 350 mm. The patient had a mastectomy with an immediate latissimus dorsi pedicled myocutaneous flap reconstruction. The breast weighed 8.27 kg, and <it>ex </it><it>vivo</it>, the tumor measured 280 mm by 250 mm by 180 mm. Histopathologic analysis confirmed the diagnosis as a giant phyllodes tumor. At 12-month follow-up, the patient reports no complications and is satisfied with the aesthetic outcome.</p> <p>Conclusion</p> <p>Giant phyllodes tumors are very rare tumors that can reach up to 40 cm in diameter. Reconstruction of such a defect is a great challenge, and we report what we believe is the first latissimus dorsi flap to cover successfully a defect of approximately 400 mm by 350 mm.</p
Electric Field Effects on Graphene Materials
Understanding the effect of electric fields on the physical and chemical
properties of two-dimensional (2D) nanostructures is instrumental in the design
of novel electronic and optoelectronic devices. Several of those properties are
characterized in terms of the dielectric constant which play an important role
on capacitance, conductivity, screening, dielectric losses and refractive
index. Here we review our recent theoretical studies using density functional
calculations including van der Waals interactions on two types of layered
materials of similar two-dimensional molecular geometry but remarkably
different electronic structures, that is, graphene and molybdenum disulphide
(MoS). We focus on such two-dimensional crystals because of they
complementary physical and chemical properties, and the appealing interest to
incorporate them in the next generation of electronic and optoelectronic
devices. We predict that the effective dielectric constant () of
few-layer graphene and MoS is tunable by external electric fields (). We show that at low fields ( V/\AA)
assumes a nearly constant value 4 for both materials, but increases at
higher fields to values that depend on the layer thickness. The thicker the
structure the stronger is the modulation of with the electric
field. Increasing of the external field perpendicular to the layer surface
above a critical value can drive the systems to an unstable state where the
layers are weakly coupled and can be easily separated. The observed dependence
of on the external field is due to charge polarization driven by
the bias, which show several similar characteristics despite of the layer
considered.Comment: Invited book chapter on Exotic Properties of Carbon Nanomatter:
Advances in Physics and Chemistry, Springer Series on Carbon Materials.
Editors: Mihai V. Putz and Ottorino Ori (11 pages, 4 figures, 30 references
Sign-reversal of the in-plane resistivity anisotropy in hole-doped iron pnictides
The in-plane anisotropy of the electrical resistivity across the coupled
orthorhombic and magnetic transitions of the iron pnictides has been
extensively studied in the parent and electron-doped compounds. All these
studies universally show that the resistivity across the long
orthorhombic axis - along which the spins couple antiferromagnetically
below the magnetic transition temperature - is smaller than the resistivity
of the short orthorhombic axis , i. e. .
Here we report that in the hole-doped compounds
BaKFeAs, as the doping level increases, the
resistivity anisotropy initially becomes vanishingly small, and eventually
changes sign for sufficiently large doping, i. e. . This
observation is in agreement with a recent theoretical prediction that considers
the anisotropic scattering of electrons by spin-fluctuations in the
orthorhombic/nematic state.Comment: This paper has been replaced by the new version offering new
explanation of the experimental results first reported her
An Evaluation of Methods for Inferring Boolean Networks from Time-Series Data
Regulatory networks play a central role in cellular behavior and decision making. Learning these regulatory networks is a
major task in biology, and devising computational methods and mathematical models for this task is a major endeavor in
bioinformatics. Boolean networks have been used extensively for modeling regulatory networks. In this model, the state of
each gene can be either âonâ or âoffâ and that next-state of a gene is updated, synchronously or asynchronously, according to
a Boolean rule that is applied to the current-state of the entire system. Inferring a Boolean network from a set of
experimental data entails two main steps: first, the experimental time-series data are discretized into Boolean trajectories,
and then, a Boolean network is learned from these Boolean trajectories. In this paper, we consider three methods for data
discretization, including a new one we propose, and three methods for learning Boolean networks, and study the
performance of all possible nine combinations on four regulatory systems of varying dynamics complexities. We find that
employing the right combination of methods for data discretization and network learning results in Boolean networks that
capture the dynamics well and provide predictive power. Our findings are in contrast to a recent survey that placed Boolean
networks on the low end of the ââfaithfulness to biological realityââ and ââability to model dynamicsââ spectra. Further, contrary
to the common argument in favor of Boolean networks, we find that a relatively large number of time points in the timeseries
data is required to learn good Boolean networks for certain data sets. Last but not least, while methods have been
proposed for inferring Boolean networks, as discussed above, missing still are publicly available implementations thereof.
Here, we make our implementation of the methods available publicly in open source at http://bioinfo.cs.rice.edu/
Rhomboid family member 2 regulates cytoskeletal stress-associated Keratin 16.
Keratin 16 (K16) is a cytoskeletal scaffolding protein highly expressed at pressure-bearing sites of the mammalian footpad. It can be induced in hyperproliferative states such as wound healing, inflammation and cancer. Here we show that the inactive rhomboid protease RHBDF2 (iRHOM2) regulates thickening of the footpad epidermis through its interaction with K16. K16 expression is absent in the thinned footpads of irhom2-/- mice compared with irhom2+/+mice, due to reduced keratinocyte proliferation. Gain-of-function mutations in iRHOM2 underlie Tylosis with oesophageal cancer (TOC), characterized by palmoplantar thickening, upregulate K16 with robust downregulation of its type II keratin binding partner, K6. By orchestrating the remodelling and turnover of K16, and uncoupling it from K6, iRHOM2 regulates the epithelial response to physical stress. These findings contribute to our understanding of the molecular mechanisms underlying hyperproliferation of the palmoplantar epidermis in both physiological and disease states, and how this 'stress' keratin is regulated
Two-channel Kondo effect and renormalization flow with macroscopic quantum charge states
Many-body correlations and macroscopic quantum behaviors are fascinating
condensed matter problems. A powerful test-bed for the many-body concepts and
methods is the Kondo model which entails the coupling of a quantum impurity to
a continuum of states. It is central in highly correlated systems and can be
explored with tunable nanostructures. Although Kondo physics is usually
associated with the hybridization of itinerant electrons with microscopic
magnetic moments, theory predicts that it can arise whenever degenerate quantum
states are coupled to a continuum. Here we demonstrate the previously elusive
`charge' Kondo effect in a hybrid metal-semiconductor implementation of a
single-electron transistor, with a quantum pseudospin-1/2 constituted by two
degenerate macroscopic charge states of a metallic island. In contrast to other
Kondo nanostructures, each conduction channel connecting the island to an
electrode constitutes a distinct and fully tunable Kondo channel, thereby
providing an unprecedented access to the two-channel Kondo effect and a clear
path to multi-channel Kondo physics. Using a weakly coupled probe, we reveal
the renormalization flow, as temperature is reduced, of two Kondo channels
competing to screen the charge pseudospin. This provides a direct view of how
the predicted quantum phase transition develops across the symmetric quantum
critical point. Detuning the pseudospin away from degeneracy, we demonstrate,
on a fully characterized device, quantitative agreement with the predictions
for the finite-temperature crossover from quantum criticality.Comment: Letter (5 pages, 4 figures) and Methods (10 pages, 6 figures
Stronger diversity effects with increased environmental stress : a study of multitrophic interactions between oak, powdery mildew and ladybirds
Recent research has suggested that increasing neighbourhood tree species diversity may mitigate the impact of pests or pathogens by supporting the activities of their natural enemies and/or reducing the density of available hosts. In this study, we attempted to assess these mechanisms in a multitrophic study system of young oak (Quercus), oak powdery mildew (PM, caused by Erysiphe spp.) and a mycophagous ladybird (Psyllobora vigintiduo-punctata). We assessed ladybird mycophagy on oak PM in function of different neighbourhood tree species compositions. We also evaluated whether these species interactions were modulated by environmental conditions as suggested by the Stress Gradient Hypothesis. We adopted a complementary approach of a field experiment where we monitored oak saplings subjected to a reduced rainfall gradient in a young planted forest consisting of different tree species mixtures, as well as a lab experiment where we independently evaluated the effect of different watering treatments on PM infections and ladybird mycophagy. In the field experiment, we found effects of neighbourhood tree species richness on ladybird mycophagy becoming more positive as the target trees received less water. This effect was only found as weather conditions grew drier. In the lab experiment, we found a preference of ladybirds to graze on infected leaves from trees that received less water. We discuss potential mechanisms that might explain this preference, such as emissions of volatile leaf chemicals. Our results are in line with the expectations of the Natural Enemies Hypothesis and support the hypothesis that biodiversity effects become stronger with increased environmental stress
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