4,183 research outputs found
Dielectric relaxation and Charge trapping characteristics study in Germanium based MOS devices with HfO2 /Dy2O3 gate stacks
In the present work we investigate the dielectric relaxation effects and
charge trapping characteristics of HfO2 /Dy2O3 gate stacks grown on Ge
substrates. The MOS devices have been subjected to constant voltage stress
(CVS) conditions at accumulation and show relaxation effects in the whole range
of applied stress voltages. Applied voltage polarities as well as thickness
dependence of the relaxation effects have been investigated. Charge trapping is
negligible at low stress fields while at higher fields (>4MV/cm) it becomes
significant. In addition, we give experimental evidence that in tandem with the
dielectric relaxation effect another mechanism- the so-called Maxwell-Wagner
instability- is present and affects the transient current during the
application of a CVS pulse. This instability is also found to be field
dependent thus resulting in a trapped charge which is negative at low stress
fields but changes to positive at higher fields.Comment: 27pages, 10 figures, 3 tables, regular journal contribution (accepted
in IEEE TED, Vol.50, issue 10
What makes a successful transition from primary to secondary school?
This report presents the findings of a sub-study on transitions undertaken as part of the
Effective Pre-school, Primary and Secondary Education 3-14 (EPPSE 3-14 project) a
major longitudinal study investigating the influence of pre-school, primary and secondary
school on children’s cognitive and social/behavioural development in England. The
transitions sub-study of more than 500 children and families sheds light on current
transition practices and highlights what helps and hinders a successful transition. It
takes into account the influence of child and family background characteristics such as
socio-economic status (SES) and gender. It suggests how the transition experience
could be improved to enhance the smooth continuity between primary and secondary
school.
By adopting a mixed methods approach, the study investigated the issues related to
transition for four distinctive groups: Local Authorities, children, parents and schools.
Officers in six Local Authorities were asked about the way transition was dealt with in
their Authority. Children in their first term at secondary school completed a
questionnaire on their thoughts and experiences of transition, and the study also sought
their parents’ opinions in order to illustrate the whole family’s experience.
Finally, there were twelve case studies selected from the respondents of the
questionnaire because of their positive experiences of transition. These involved
interviews with the children and their primary and secondary teachers. This provided
further details of the systems in place that support the transition processes between
school phases.
The sample was drawn from children and families in the wider EPPSE project. 1190
children from the EPPSE sample made a transition at the end of the 2005-06 academic
year. Responses were received from 550 children (a 46% response rate) and 569
parents (a 48% response rate) from across England drawn from 6 Local Authorities
(Shire County, Inner London borough, Midlands/Metropolitan region, East Anglia area,
and two authorities in the North East). Children were recruited to the case studies using
stratified selection to get a balanced mix by region, gender, socio-economic status (SES)
and ethnicity. A wide range of data, already available from the main EPPSE study was
used to complement the analyses
Gate Stack Dielectric Degradation of Rare-Earth Oxides Grown on High Mobility Ge Substrates
We report on the dielectric degradation of Rare-Earth Oxides (REOs), when
used as interfacial buffer layers together with HfO2 high-k films (REOs/HfO2)
on high mobility Ge substrates. Metal-Oxide-Semiconductor (MOS) devices with
these stacks,show dissimilar charge trapping phenomena under varying levels of
Constant- Voltage-Stress (CVS) conditions, which also influences the measured
densities of the interface (Nit) and border (NBT) traps. In the present study
we also report on C-Vg hysteresis curves related to Nit and NBT. We also
propose a new model based on Maxwell-Wagner instabilities mechanism that
explains the dielectric degradations (current decay transient behavior) of the
gate stack devices grown on high mobility substrates under CVS bias from low to
higher fields, and which is unlike to those used for other MOS devices.
Finally, the time dependent degradation of the corresponding devices revealed
an initial current decay due to relaxation, followed by charge trapping and
generation of stress-induced leakage which eventually lead to hard breakdown
after long CVS stressing.Comment: 19pages (double space), 7 figures, original research article,
Submitted to JAP (AIP
Two Interacting Electrons in a Quasiperiodic Chain
We study numerically the effect of on-site Hubbard interaction U between two
electrons in the quasiperiodic Harper's equation. In the periodic chain limit
by mapping the problem to that of one electron in two dimensions with a
diagonal line of impurities of strength U we demonstrate a band of resonance
two particle pairing states starting from E=U. In the ballistic (metallic)
regime we show explicitly interaction-assisted extended pairing states and
multifractal pairing states in the diffusive (critical) regime. We also obtain
localized pairing states in the gaps and the created subband due to U, whose
number increases when going to the localized regime, which are responsible for
reducing the velocity and the diffusion coefficient in the qualitatively
similar to the non-interacting case ballistic and diffusive dynamics. In the
localized regime we find propagation enhancement for small U and stronger
localization for larger U, as in disordered systems.Comment: 14 pages Revtex file, 8 figures (split into 19 jpg figures).
(postscript versions of the jpg figures are also available upon request)
submitted to PR
A Body Shape Index (ABSI), hip index and risk of cancer in the UK Biobank cohort
Abdominal size is associated positively with the risk of some cancers but the influence of body mass index (BMI) and gluteofemoral size is unclear because waist and hip circumference are strongly correlated with BMI. We examined associations of 33 cancers with A Body Shape Index (ABSI) and hip index (HI), which are independent of BMI by design, and compared these with waist and hip circumference, using multivariable Cox proportional hazards models in UK Biobank. During a mean follow up of seven years, 14,682 incident cancers were ascertained in 200,289 men and 12,965 cancers in 230,326 women. In men, ABSI was associated positively with cancers of the head and neck (hazard ratio HR=1.14; 95% confidence interval 1.03-1.26 per one standard deviation increment), oesophagus (adenocarcinoma, HR=1.27; 1.12-1.44), gastric cardia (HR=1.31; 1.07-1.61), colon (HR=1.18; 1.10-1.26), rectum (HR=1.13; 1.04-1.22), lung (adenocarcinoma, HR=1.16; 1.03-1.30; squamous-cell carcinoma (SCC), HR=1.33; 1.17-1.52), and bladder (HR=1.15; 1.04-1.27), while HI was associated inversely with cancers of the oesophagus (adenocarcinoma, HR=0.89; 0.79-1.00), gastric cardia (HR=0.79; 0.65-0.96), colon (HR=0.92; 0.86-0.98), liver (HR=0.86; 0.75-0.98), and multiple myeloma (HR=0.86; 0.75-1.00). In women, ABSI was associated positively with cancers of the head and neck (HR=1.27; 1.10-1.48), oesophagus (SCC, HR=1.37; 1.07-1.76), colon (HR=1.08; 1.01-1.16), lung (adenocarcinoma, HR=1.17; 1.06-1.29; SCC, HR=1.40; 1.20-1.63; small-cell, HR=1.39; 1.14-1.69), kidney (clear-cell, HR=1.25; 1.03-1.50), and post-menopausal endometrium (HR=1.11; 1.02-1.20), while HI was associated inversely with skin SCC (HR=0.91; 0.83-0.99), post-menopausal kidney cancer (HR=0.77; 0.67-0.88) and post-menopausal melanoma (HR=0.90; 0.83-0.98). Unusually, ABSI was associated inversely with melanoma in men (HR=0.89; 0.82-0.96) and pre-menopausal women (HR=0.77; 0.65-0.91). Waist and hip circumference reflected associations with BMI, when examined individually, and provided biased risk estimates, when combined with BMI. In conclusion, preferential positive associations of ABSI or inverse of HI with several major cancers indicate an important role of factors determining body shape in cancer development
The struggle of a good friend getting old:cellular senescence in viral responses and therapy
Cellular senescence is a state of stable cell cycle arrest associated with macromolecular alterations and secretion of pro-inflammatory cytokines and molecules. Senescence-associated phenotypes restrict damage propagation and activate immune responses, two essential processes involved in response to viral infections. However, excessive accumulation and persistence of senescent cells can become detrimental and promote pathology and dysfunctions. Various pharmacological interventions, including antiviral therapies, lead to aberrant and premature senescence. Here, we review the molecular mechanisms by which viral infections and antiviral therapy induce senescence. We highlight the importance of these processes in attenuating viral dissemination and damage propagation, but also how prematurely induced senescent cells can promote detrimental adverse effects in humans. We describe which sequelae due to viral infections and treatment can be partly due to excessive and aberrant senescence. Finally, we propose that pharmacological strategies which eliminate senescent cells or suppress their secretory phenotype could mitigate side effects and alleviate the onset of additional morbidities. These strategies can become extremely beneficial in patients recovering from viral infections or undergoing antiviral therapy
Conductance fluctuations and boundary conditions
The conductance fluctuations for various types for two-- and
three--dimensional disordered systems with hard wall and periodic boundary
conditions are studied, all the way from the ballistic (metallic) regime to the
localized regime. It is shown that the universal conductance fluctuations (UCF)
depend on the boundary conditions. The same holds for the metal to insulator
transition. The conditions for observing the UCF are also given.Comment: 4 pages RevTeX, 5 figures include
Anderson transition in three-dimensional disordered systems with symplectic symmetry
The Anderson transition in a 3D system with symplectic symmetry is
investigated numerically. From a one-parameter scaling analysis the critical
exponent of the localization length is extracted and estimated to be . The level statistics at the critical point are also analyzed
and shown to be scale independent. The form of the energy level spacing
distribution at the critical point is found to be different from that
for the orthogonal ensemble suggesting that the breaking of spin rotation
symmetry is relevant at the critical point.Comment: 4 pages, revtex, to appear in Physical Review Letters. 3 figures
available on request either by fax or normal mail from
[email protected] or [email protected]
Critical level spacing distribution of two-dimensional disordered systems with spin-orbit coupling
The energy level statistics of 2D electrons with spin-orbit scattering are
considered near the disorder induced metal-insulator transition. Using the Ando
model, the nearest-level-spacing distribution is calculated numerically at the
critical point. It is shown that the critical spacing distribution is size
independent and has a Poisson-like decay at large spacings as distinct from the
Gaussian asymptotic form obtained by the random-matrix theory.Comment: 7 pages REVTeX, 2 uuencoded, gzipped figures; J. Phys. Condensed
Matter, in prin
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