503 research outputs found
High pressure diamond-like liquid carbon
We report density-functional based molecular dynamics simulations, that show
that, with increasing pressure, liquid carbon undergoes a gradual
transformation from a liquid with local three-fold coordination to a
'diamond-like' liquid. We demonstrate that this unusual structural change is
well reproduced by an empirical bond order potential with isotropic long range
interactions, supplemented by torsional terms. In contrast, state-of-the-art
short-range bond-order potentials do not reproduce this diamond structure. This
suggests that a correct description of long-range interactions is crucial for a
unified description of the solid and liquid phases of carbon.Comment: 4 pages, 5 figure
Magnetic contrast agents for optical coherence tomography
The magneto-mechanical effect is exploited as a means of producing background-free contrast in optical coherence tomography (OCT). Contrast agents consisting of iron-oxide particles and protein microspheres encapsulating colloidal iron-oxide have a sufficiently high magnetic susceptibility to be detected by modulation of a magnetic field gradient using a small solenoid coil. The externally-applied magnetic field mechanically rotates or translates these highly scattering contrast agents within the sample at the modulation frequency, which is subsequently detected as amplitude modulation of the OCT signal. Pairs of sequential axial scans (A-lines) are acquired with the magnetic field on and off, allowing one to build up a pair of images corresponding to the "on" and "off" states of the magnetic field. These image pairs are differenced to look for magnetic-specific effects, allowing one to distinguish the magnetic contrast agents from non-magnetic structures within the sample with a signal-to-background ratio of âŒ23dB. This technique has the potential to be very powerful when coupled with targeting for in vivo molecular imaging. To evaluate this potential we demonstrate in vitro imaging of magnetically-labeled macrophage cells embedded in a 3D tissue phantom, in vitro tissue doped with contrast agents, and in vivo imaging of Xenopus laevis (African frog) tadpoles
The future of sovereignty in multilevel governance Europe: a constructivist reading
Multilevel governance presents a depiction of contemporary structures in EU Europe as consisting of overlapping authorities and competing competencies. By focusing on emerging non-anarchical structures in the international system, hence moving beyond the conventional hierarchy/anarchy dichotomy to distinguish domestic and international arenas, this seems a radical transformation of the familiar Westphalian system and to undermine state sovereignty. Paradoxically, however, the principle of sovereignty proves to be resilient despite its alleged empirical decline. This article argues that social constructivism can explain the paradox, by considering sovereign statehood as a process-dependent institutional fact, and by showing that multilevel governance can feed into this process
Split-off dimer defects on the Si(001)2x1 surface
Dimer vacancy (DV) defect complexes in the Si(001)2x1 surface were
investigated using high-resolution scanning tunneling microscopy and first
principles calculations. We find that under low bias filled-state tunneling
conditions, isolated 'split-off' dimers in these defect complexes are imaged as
pairs of protrusions while the surrounding Si surface dimers appear as the
usual 'bean-shaped' protrusions. We attribute this to the formation of pi-bonds
between the two atoms of the split-off dimer and second layer atoms, and
present charge density plots to support this assignment. We observe a local
brightness enhancement due to strain for different DV complexes and provide the
first experimental confirmation of an earlier prediction that the 1+2-DV
induces less surface strain than other DV complexes. Finally, we present a
previously unreported triangular shaped split-off dimer defect complex that
exists at SB-type step edges, and propose a structure for this defect involving
a bound Si monomer.Comment: 8 pages, 7 figures, submitted to Phys. Rev.
Application of multivariate techniques in the evaluation of melt granulation products
In this work, principal component analysis and cluster analysis were applied as helping tools to extract useful information in the development of formulations and manufacturing processes of melt granulates. Two melt granulation processes that differ in the shear stress applied to the solid bed during melting step were designed. These processes employ equipment frequently used in the local pharmaceutical industry. The selected binders include both hydrophilic and hydrophobic excipients, which were used alone or in binary mixtures. Granulates were characterized regarding their physicomechanical properties, including their compaction behavior. The resulting tablets were also evaluated. The selected multivariate statistical methods proved to be useful in facilitating the interpretation of the collected data and the study of the properties of granulates and tablets, as well as the selection of more efficient production processes.Neste trabalho, foram aplicadas as tĂ©cnicas de anĂĄlise de componentes principais e de anĂĄlise de agrupamentos para extrair informaçÔes Ășteis no desenvolvimento de formulaçÔes e de processos de produção de granulados por fusĂŁo. Desenharam-se dois processos de granulação por fusĂŁo que apresentam diferenças na tensĂŁo de cisalhamento aplicada ao leito sĂłlido durante a etapa de fusĂŁo. Esses processos empregam equipamentos frequentemente usados na indĂșstria farmacĂȘutica local. Os ligantes escolhidos incluĂram excipientes tanto hidrofĂlicos quanto hidrofĂłbicos, utilizados de forma individual ou em misturas binĂĄrias. Os granulados foram caracterizados quanto Ă s suas propriedades fĂsico-mecĂąnicas, incluindo seu desempenho no processo de compactação. Os comprimidos resultantes tambĂ©m foram avaliados. Os mĂ©todos de anĂĄlise multivariada escolhidos provaram ser Ășteis para facilitar a interpretação dos dados coletados e o estudo das propriedades dos granulados e dos comprimidos, bem como a seleção de processos de produção mais eficientes
Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA
An investigation of the hadronic final state in diffractive and
non--diffractive deep--inelastic electron--proton scattering at HERA is
presented, where diffractive data are selected experimentally by demanding a
large gap in pseudo --rapidity around the proton remnant direction. The
transverse energy flow in the hadronic final state is evaluated using a set of
estimators which quantify topological properties. Using available Monte Carlo
QCD calculations, it is demonstrated that the final state in diffractive DIS
exhibits the features expected if the interaction is interpreted as the
scattering of an electron off a current quark with associated effects of
perturbative QCD. A model in which deep--inelastic diffraction is taken to be
the exchange of a pomeron with partonic structure is found to reproduce the
measurements well. Models for deep--inelastic scattering, in which a
sizeable diffractive contribution is present because of non--perturbative
effects in the production of the hadronic final state, reproduce the general
tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil
A Search for Selectrons and Squarks at HERA
Data from electron-proton collisions at a center-of-mass energy of 300 GeV
are used for a search for selectrons and squarks within the framework of the
minimal supersymmetric model. The decays of selectrons and squarks into the
lightest supersymmetric particle lead to final states with an electron and
hadrons accompanied by large missing energy and transverse momentum. No signal
is found and new bounds on the existence of these particles are derived. At 95%
confidence level the excluded region extends to 65 GeV for selectron and squark
masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure
The differential diagnosis of chronic daily headaches: an algorithm-based approach
Chronic daily headaches (CDHs) refers to primary headaches that happen on at least 15 days per month, for 4 or more hours per day, for at least three consecutive months. The differential diagnosis of CDHs is challenging and should proceed in an orderly fashion. The approach begins with a search for âred flagsâ that suggest the possibility of a secondary headache. If secondary headaches that mimic CDHs are excluded, either on clinical grounds or through investigation, the next step is to classify the headaches based on the duration of attacks. If the attacks last less than 4 hours per day, a trigeminal autonomic cephalalgia (TAC) is likely. TACs include episodic and chronic cluster headache, episodic and chronic paroxysmal hemicrania, SUNCT, and hypnic headache. If the duration is â„4 h, a CDH is likely and the differential diagnosis encompasses chronic migraine, chronic tension-type headache, new daily persistent headache and hemicrania continua. The clinical approach to diagnosing CDH is the scope of this review
- âŠ