811 research outputs found
An Analysis of Profit Cycles in the Airline Industry
This paper discusses the financial dynamics of the airline industry by
identifying the fundamental cycle periods of profitability and their driving factors.
Assuming the industry profit cycles could be modeled as an undamped second-order system,
the fundamental cycle period was found to be 11.3 years for the U.S. airline industry and
10.5 years for the world airline industry. An empirical profitability model was estimated and
the results revealed that such cycle period is endogenous, neither deregulation nor
September 11 have significantly changed the cycle length. To analyze the causes of profit
cyclicality, parametric models were developed under the hypothesis that phase lag in the
system caused the profit oscillations; and two hypotheses, lag in capacity response and lag in
cost adjustment were studied. Analysis of the parametric model of capacity response
indicated that the system stability depends on the delay between aircraft orders and
deliveries and on the aggressiveness in airplane ordering. Exaggerated capacity response
was observed in the simulation as the gain in the model has lumped impacts of exogenous
factors, suggesting capacity shortfall alone cannot fully explain the industry dynamics. The
model also indicates reducing delay may help to mitigate system oscillations. Simulation
results of the parametric model regarding cost adjustment were consistent with profit
observations. Finally, a coupled model was developed to study the joint effects of capacity
and cost. Simulation results indicated that the coupled model explained industry dynamics
better than individual capacity or cost models, suggesting that the system behavior is driven
by the joint effects of capacity response and cost adjustment
Stakeholder Attitudes towards Wildlife-Based Land Use in Namibia’s Kunene Region
African rangeland systems are characterized by competing resource use for livestock farming and wildlife conservation. In Namibia’s rangeland savannahs, cattle farming for commercial and subsistence purposes is common, shaping the land use system of the country’s north. Local cattle stocking rates increased over the past decades and triggered ecosystem degradation that became visible in the last drought-stricken years. Cattle was lost, meat prices dropped and livelihoods were threatened. It is assumed that current land use activities are pushing the rangeland ecosystem towards ecological tipping points. Alternative approaches to use the scarce resources of rangelands in a more sustainable way may be centred on wildlife-based land use strategies.
Against this background, we investigate the attitudes of stakeholders towards wildlife in order to carve out current barriers for upscaling wildlife-based land use strategies. We conducted stakeholder mapping based on the results of a larger qualitative survey, which included a workshop, individual interviews and a participatory observation. Our results indicate that the reasons for stakeholders being hesitant towards wildlife-based strategies can be clustered around (i) cultural and traditional practices, (ii) unfavourable market conditions and (iii) negative connotations of certain wildlife utilization practices. The study results contribute to the identification of entry points for policies that seek to support wildlife-based strategies
Single And Double-electron Removal From H− In Energetic Collisions With Multiply-charged Argon Ions
Absolute cross-sections have been measured and compared to CTMC-calculations for single and double-electron removal from H− in collisions with Arq+ ions (q ≤ 8) at Ec.m. = 50 keV. The single-electron removal cross-sections are found to scale with q1.3, and for the H− + Ar4+ system, this cross-section is found to have a weak energy dependence from 3 keV to 100 keV. A major implication of our measurements is that plasma neutralizers based on multiply charged ions for high-efficiency conversion of intense H− beams into H0 gain little in expected reduced length due to the inapplicability of q2-scaling in the H− single-electron removal cross-section. © 1989, IOP Publishing Ltd
In-Line-Test of Variability and Bit-Error-Rate of HfOx-Based Resistive Memory
Spatial and temporal variability of HfOx-based resistive random access memory
(RRAM) are investigated for manufacturing and product designs. Manufacturing
variability is characterized at different levels including lots, wafers, and
chips. Bit-error-rate (BER) is proposed as a holistic parameter for the write
cycle resistance statistics. Using the electrical in-line-test cycle data, a
method is developed to derive BERs as functions of the design margin, to
provide guidance for technology evaluation and product design. The proposed BER
calculation can also be used in the off-line bench test and build-in-self-test
(BIST) for adaptive error correction and for the other types of random access
memories.Comment: 4 pages. Memory Workshop (IMW), 2015 IEEE Internationa
About the origin of the acrocentric part of non-acrocentric satellited chromosomes in humans
Here we characterized 11 healthy carriers of a non-acrocentric satellited chromosomes der(A)t(A;acro)(pter or qter;p1?1.2) to determine the frequency of chromosome 15p and 22p in such rearrangement
First molecular cytogenetic characterization of the MMT 060562 murine breast cancer cell line
To provide detailed cytogenetic characterization of the MMT 060562 cancer cell lin
Spin Driven Jahn-Teller Distortion in a Pyrochlore system
The ground-state properties of the spin-1 antiferromagnetic Heisenberg model
on the corner-sharing tetrahedra, pyrochlore lattice, is investigated. By
breaking up each spin into a pair of 1/2-spins, the problem is reduced to the
equivalent one of the spin-1/2 tetrahedral network in analogy with the valence
bond solid state in one dimension. The twofold degeneracy of the spin-singlets
of a tetrahedron is lifted by a Jahn-Teller mechanism, leading to a cubic to
tetragonal structural transition. It is proposed that the present mechanism is
responsible for the phase transition observed in the spin-1 spinel compounds
ZnVO and MgVO.Comment: 4 pages, 3 eps figures, REVTeX, to appear in Phys. Rev. Let
X-chromosome terminal deletion in a female with premature ovarian failure: Haploinsufficiency of X-linked genes as a possible explanation
<p>Abstract</p> <p>Background</p> <p>Premature ovarian failure (POF) has repeatedly been associated to X-chromosome deletions. <it>FMR1 </it>gene premutation allele's carrier women have an increased risk for POF. We intent to determine the cause of POF in a 29 year old female, evaluating both of these situations.</p> <p>Methods</p> <p>Concomitant analysis of <it>FMR1 </it>gene CGG repeat number and karyotype revealed an X-chromosome terminal deletion. Fluorescence <it>in situ </it>further characterized the breakpoint. A methylation assay for <it>FMR1 </it>gene allowed to determine its methylation status, and hence, the methylation status of the normal X-chromosome.</p> <p>Results</p> <p>We report a POF patient with a 46,X,del(X)(q26) karyotype and with skewed X-chromosome inactivation of the structural abnormal X-chromosome.</p> <p>Conclusions</p> <p>Despite the hemizygosity of <it>FMR1 </it>gene, the patient does not present Fragile X syndrome features, since the normal X-chromosome is not subject to methylation. The described deletion supports the hypothesis that haploinsufficiency of X-linked genes can be on the basis of POF, and special attention should be paid to X-linked genes in region Xq28 since they escape inactivation and might have a role in this disorder. A full clinical and cytogenetic characterization of all POF cases is important to highlight a pattern and help to understand which genes are crucial for normal ovarian development.</p
Ion Energy Measurements in Plasma Immersion Ion Implantation
This thesis investigates ion energy distributions (IEDs) during plasma immersion ion implantation (PIII). PIII is a surface modification technique where an object is placed in a plasma and pulse biased with large negative voltages. The energy distribution of implanted ions is important in determining the extent of surface modifications. IED measurements were made during PIII using a pulse biased retarding field energy analyser (RFEA) in a capacitive RF plasma. Experimental results were compared with those obtained from a two dimensional numerical simulation to help explain the origins of features in the IEDs. Time resolved IED measurements were made during PIII of metal and insulator materials and investigated the effects of the use of a metal mesh over the surface and the effects of insulator surface charging. When the pulse was applied to the RFEA, the ion flux rapidly increased above the pulse-off value and then slowly decreased during the pulse. The ion density during the pulse decreased below values measured when no pulse was applied to the RFEA. This indicates that the depletion of ions by the pulsed RFEA is greater than the generation of ions in the plasma. IEDs measured during pulse biasing showed a peak close to the maximum sheath potential energy and a spread of ions with energies between zero and the maximum ion energy. Simulations showed that the peak is produced by ions from the sheath edge directly above the RFEA inlet and that the spread of ions is produced by ions which collide in the sheath and/or arrive at the RFEA with trajectories not perpendicular to the RFEA front surface. The RFEA discriminates ions based only on the component of their velocity perpendicular to the RFEA front surface. To minimise the effects of surface charging during PIII of an insulator, a metal mesh can be placed over the insulator and pulse biased together with the object. Measurements were made with metal mesh cylinders fixed to the metal RFEA front surface. The use of a mesh gave a larger ion flux compared to the use of no mesh. The larger ion flux is attributed to the larger plasma-sheath surface area around the mesh. The measured IEDs showed a low, medium and high energy peak. Simulation results show that the high energy peak is produced by ions from the sheath above the mesh top. The low energy peak is produced by ions trapped by the space charge potential hump which forms inside the mesh. The medium energy peak is produced by ions from the sheath above the mesh corners. Simulations showed that the IED is dependent on measurement position under the mesh. To investigate the effects of insulator surface charging during PIII, IED measurements were made through an orifice cut into a Mylar insulator on the RFEA front surface. With no mesh, during the pulse, an increasing number of lower energy ions were measured. Simulation results show that this is due to the increase in the curvature of the sheath over the orifice region as the insulator potential increases due to surface charging. The surface charging observed at the insulator would reduce the average energy of ions implanted into the insulator during the pulse. Compared to the case with no mesh, the use of a mesh increases the total ion flux and the ion flux during the early stages of the pulse but does not eliminate surface charging. During the pulse, compared to the no mesh case, a larger number of lower energy ions are measured. Simulation results show that this is caused by the potential in the mesh region which affects the trajectories of ions from the sheaths above the mesh top and corners and results in more ions being measured with trajectories less than ninety degrees to the RFEA front surface
Characterization of a prenatally assessed de novo supernumerary minute ring chromosome 20 in a phenotypically normal male
<p>Abstract</p> <p>Background</p> <p>The heterogeneous group of small supernumerary marker chromosomes (sSMCs) presents serious counseling problems, especially if they are present de novo and diagnosed prenatally. The incidence has been estimated at 1 in 1000 prenatal samples. We present a case of mosaic sSMC diagnosed prenatally after amniocentesis. The sSMC was characterized by various molecular cytogenetic techniques and determined to be a r(20) chromosome. After genetic counseling, the parents decided to continue the pregnancy, and a boy with minor phenotypic variants was born after 39 weeks of pregnancy. The case is compared with four other cases of prenatally detected r(20) mosaicism.</p> <p>Results</p> <p>Here we describe a 3 months old male child with normal pre- and postnatal development and with a de novo ring supernumerary marker chromosome in amniocytes cultures. Using new fluorescence in situ hybridization (FISH) techniques, three distinguishable sSMCs (cryptic mosaicism), all derived from chromosome 20, were observed, including ring and minute chromosomes. This heterogeneity was impossible to detect by the conventional G-banding technique or conventional FISH technique that were used before the application of new FISH techniques (subcentromere-specific multicolor-FISH [subcenM-FISH]) and a probe, specific for the 20p12.2 band. The sSMC present in 25% of the cells was present as r(20)(::p12.2~12.3->q11.1::)<abbrgrp><abbr bid="B5">5</abbr></abbrgrp>/r(20;20)(::p12.1->q11.1::q11.1 >p12.1::)<abbrgrp><abbr bid="B2">2</abbr></abbrgrp>/min(20;20)(:p12.1->q11.1::q11.1->p12.1:)<abbrgrp><abbr bid="B1">1</abbr></abbrgrp>. The final karyotype was 47,XY,+r(20)[25%]/46,XY[75%].</p> <p>Conclusion</p> <p>We emphasize the importance of application of molecular cytogenetics in a prenatally diagnostic laboratory and description of more cases to enable a better genetic counseling and risk evaluation.</p
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