534 research outputs found
The impact of short-selling in financial markets
This dissertation empirically examines the impact of short-selling in financial markets. Given the increasing participation of short-sellers in financial markets, this research provides empirical evidence on an increasingly important issue. Each chapter addresses a research question with scarce or conflicting prior research findings to provide evidence which can assist researchers, investors and regulators to understand and manage the impact of short-selling in financial markets
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New Measures for Predicting Birth-Related Pelvic Floor Trauma.
OBJECTIVES: The aim of this study was to establish the predictive role of obstetric variables for obstetric outcomes and birth related levator ani muscle (LAM) trauma. METHODS: In this prospective study, women underwent 3-dimensional pelvic floor ultrasound at their first appointment at 36 weeks and also 3 months postpartum. The measurements included minimal levator hiatus circumference (MLHC) and the ratio of fetal head circumference to MLHC = head-induced stretch ratio (HISR) as an indicator of the discrepancy between passage and passing canal. To derive the true impact of baby's mass on the levator ani musculature, we devised the levator ani stretch ratio (LASR), which was calculated by multiplying the HISR and the baby's weight. RESULTS: Data set of 173 women was available for analysis. Mean HISR and LASR values were statistically different across all binary outcome categories, with 1 exception for HISR and levator ani injury. The odds ratios for LASR indicated positive and statistically significant associations with all obstetric outcomes examined. The probability of the LASR correctly classifying those with the adverse obstetric outcome, as estimated by the area under the curve, ranged from 0.64 to 0.80 with the strongest discriminatory ability observed for severe LAM trauma. CONCLUSIONS: Fetal head circumference/mother MLHC ratio (HISR) is associated with longer length of second stage of labor, assisted delivery, and increased severity of perineal trauma. Similar associations were observed for LASR, but in addition, LASR had good discriminatory ability to identify severe LAM trauma
The relationship between physical and psychological complaints and quality of life in severely injured patients
Purpose: The purpose of this study was two-fold. The first goal was to investigate which variables were associated with the remaining physical limitations of severely injured patients after the initial rehabilitation phase. Second, we investigated whether physical limitations were attributable to the association between psychological complaints and quality of life in this patient group. Methods: Patients who were 18 years or older and who had an injury severity score (ISS). >. 15 completed a set of questionnaires at one time-point after their rehabilitation phase (15-53 months after their trauma). The Short Musculoskeletal Function Assessment (SMFA) questionnaire was used to determine physical limitations. The Hospital Anxiety and Depression Scale, the Dutch Impact of Event Scale and the Cognitive Failure Questionnaire were used to determine psychological complaints, and the World Health Organization Quality of Life assessment instrument-BREF was used to measure general Quality of Life (QOL).Differences in physical limitations were investigated for several trauma- and patient-related variables using non-parametric independent-sample Mann-Whitney U tests. Multiple linear regression was performed to investigate whether the decreased QOL of severely injured patients with psychological complaints could be explained by their physical limitations. Results: Older patients, patients with physical complaints before the injury, patients with higher ISS scores, and patients who had an injury of the spine or of the lower extremities reported significantly more physical problems. Additionally, patients with a low education level, patients who were living alone, and those who were unemployed reported significantly more long-term physical problems.Severely injured patients without psychological complaints reported significantly less physical limitations than those with psychological complaints. The SMFA factor of Lower extremity dysfunctio
Forced Imbibition - a Tool for Determining Laplace Pressure, Drag Force and Slip Length in Capillary Filling Experiments
When a very thin capillary is inserted into a liquid, the liquid is sucked
into it: this imbibition process is controlled by a balance of capillary and
drag forces, which are hard to quantify experimentally, in particularly
considering flow on the nanoscale. By computer experiments using a generic
coarse-grained model, it is shown that an analysis of imbibition forced by a
controllable external pressure quantifies relevant physical parameter such as
the Laplace pressure, Darcy's permeability, effective pore radius, effective
viscosity, dynamic contact angle and slip length of the fluid flowing into the
pore. In determining all these parameters independently, the consistency of our
analysis of such forced imbibition processes is demonstrated.Comment: 4 pages, 5 figure
Dephasing in Metals by Two-Level Systems in the 2-Channel-Kondo Regime
We point out a novel, non-universal contribution to the dephasing rate
1/\tau_\phi \equiv \gamma_\phi of conduction electrons in metallic systems:
scattering off non-magnetic two-level systems (TLSs) having almost degenerate
Kondo ground states. In the regime \Delta_{ren} < T < T_K (\Delta_{ren} =
renormalized level splitting, T_K = Kondo temperature), such TLSs exhibit
non-Fermi-liquid physics that can cause \gamma_\phi, which generally decreases
with decreasing T, to seemingly saturate in a limited temperature range before
vanishing for T \to 0. This could explain the saturation of dephasing recently
observed in gold wires [Mohanty et al. Phys. Rev. Lett. 78, 3366 (1997)].Comment: Final published version, including minor improvements suggested by
referees. 4 pages, Revtex, 1 figur
Oscillatory Tunnel Splittings in Spin Systems: A Discrete Wentzel-Kramers-Brillouin Approach
Certain spin Hamiltonians that give rise to tunnel splittings that are viewed
in terms of interfering instanton trajectories, are restudied using a discrete
WKB method, that is more elementary, and also yields wavefunctions and
preexponential factors for the splittings. A novel turning point inside the
classically forbidden region is analysed, and a general formula is obtained for
the splittings. The result is appled to the \Fe8 system. A previous result for
the oscillation of the ground state splitting with external magnetic field is
extended to higher levels.Comment: RevTex, one ps figur
Transport properties and point contact spectra of Ni_xNb_{1-x} metallic glasses
Bulk resistivity and point contact spectra of Ni_xNb_{1-x} metallic glasses
have been investigated as functions of temperature (0.3-300K) and magnetic
field (0-12T). Metallic glasses in this family undergo a superconducting phase
transition determined by the Nb concentration. When superconductivity was
suppressed by a strong magnetic field, both the bulk sample R(T) and the point
contact differential resistance curves of Ni_xNb_{1-x} showed logarithmic
behavior at low energies, which is explained by a strong electron - "two level
system" coupling. We studied the temperature, magnetic field and contact
resistance dependence of Ni_{44}Nb_{56} point-contact spectra in the
superconducting state and found telegraph-like fluctuations superimposed on
superconducting characteristics. These R(V) characteristics are extremely
sensitive detectors for slow relaxing "two level system" motion.Comment: 4 pages, 5 figure
Free radical scavenging and formation by multi-walled carbon nanotubes in cell free conditions and in human bronchial epithelial cells
Background:
Certain multi-walled carbon nanotubes (MWCNTs) have been shown to elicit asbestos-like toxicological effects. To reduce needs for risk assessment it has been suggested that the physicochemical characteristics or reactivity of nanomaterials could be used to predict their hazard. Fibre-shape and ability to generate reactive oxygen species (ROS) are important indicators of high hazard materials. Asbestos is a known ROS generator, while MWCNTs may either produce or scavenge ROS. However, certain biomolecules, such as albumin – used as dispersants in nanomaterial preparation for toxicological testing in vivo and in vitro - may reduce the surface reactivity of nanomaterials.
Methods:
Here, we investigated the effect of bovine serum albumin (BSA) and cell culture medium with and without BEAS 2B cells on radical formation/scavenging by five MWCNTs, Printex 90 carbon black, crocidolite asbestos, and glass wool, using electron spin resonance (ESR) spectroscopy and linked this to cytotoxic effects measured by trypan blue exclusion assay. In addition, the materials were characterized in the exposure medium (e.g. for hydrodynamic size-distribution and sedimentation rate).
Results:
The test materials induced highly variable cytotoxic effects which could generally be related to the abundance and characteristics of agglomerates/aggregates and to the rate of sedimentation. All carbon nanomaterials were found to scavenge hydroxyl radicals (•OH) in at least one of the solutions tested. The effect of BSA was different among the materials. Two types of long, needle-like MWCNTs (average diameter >74 and 64.2 nm, average length 5.7 and 4.0 µm, respectively) induced, in addition to a scavenging effect, a dose-dependent formation of a unique, yet unidentified radical in both absence and presence of cells, which also coincided with cytotoxicity.
Conclusions:
Culture medium and BSA affects scavenging/production of •OH by MWCNTs, Printex 90 carbon black, asbestos and glass-wool. An unidentified radical is generated by two long, needle-like MWCNTs and these two CNTs were more cytotoxic than the other CNTs tested, suggesting that this radical could be related to the adverse effects of MWCNTs
Quenched Spin Tunneling and Diabolical Points in Magnetic Molecules: II. Asymmetric Configurations
The perfect quenching of spin tunneling first predicted for a model with
biaxial symmetry, and recently observed in the magnetic molecule Fe_8, is
further studied using the discrete phase integral (or
Wentzel-Kramers-Brillouin) method. The analysis of the previous paper is
extended to the case where the magnetic field has both hard and easy
components, so that the Hamiltonian has no obvious symmetry. Herring's formula
is now inapplicable, so the problem is solved by finding the wavefunction and
using connection formulas at every turning point. A general formula for the
energy surface in the vicinity of the diabolo is obtained in this way. This
formula gives the tunneling apmplitude between two wells unrelated by symmetry
in terms of a small number of action integrals, and appears to be generally
valid, even for problems where the recursion contains more than five terms.
Explicit results are obtained for the diabolical points in the model for Fe_8.
These results exactly parallel the experimental observations. It is found that
the leading semiclassical results for the diabolical points appear to be exact,
and the points themselves lie on a perfect centered rectangular lattice in the
magnetic field space. A variety of evidence in favor of this perfect lattice
hypothesis is presented.Comment: Revtex; 4 ps figures; follow up to cond-mat/000311
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