255 research outputs found
Microscopic modelling of perpendicular electronic transport in doped multiple quantum wells
We present a microscopic calculation of transport in strongly doped
superlattices where domain formation is likely to occur. Our theoretical method
is based on a current formula involving the spectral functions of the system,
and thus allows, in principle, a systematic investigation of various
interaction mechanisms. Taking into account impurity scattering and optical
phonons we obtain a good quantitative agreement with existing experimental data
from Helgesen and Finstad (J. Appl. Phys. 69, 2689, (1991)). Furthermore the
calculated spectral functions indicate a significant increase of the average
intersubband spacing compared to the bare level differences which might explain
the experimental trend.Comment: 10 pages 5 figure
Dynamic roughening and fluctuations of dipolar chains
Nonmagnetic particles in a carrier ferrofluid acquire an effective dipolar
moment when placed in an external magnetic field. This fact leads them to form
chains that will roughen due to Brownian motion when the magnetic field is
decreased. We study this process through experiments, theory and simulations,
three methods that agree on the scaling behavior over 5 orders of magnitude.
The RMS width goes initially as , then as before it
saturates. We show how these results complement existing results on polymer
chains, and how the chain dynamics may be described by a recent non-Markovian
formulation of anomalous diffusion.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Theory of commensurable magnetic structures in holmium
The tendency for the period of the helically ordered moments in holmium to
lock into values which are commensurable with the lattice is studied
theoretically as a function of temperature and magnetic field. The
commensurable effects are derived in the mean-field approximation from
numerical calculations of the free energy of various commensurable structures,
and the results are compared with the extensive experimental evidence collected
during the last ten years on the magnetic structures in holmium. In general the
stability of the different commensurable structures is found to be in accord
with the experiments, except for the tau=5/18 structure observed a few degrees
below T_N in a b-axis field. The trigonal coupling recently detected in holmium
is found to be the interaction required to explain the increased stability of
the tau=1/5 structure around 42 K, and of the tau=1/4 structure around 96 K,
when a field is applied along the c-axis.Comment: REVTEX, 31 pages, 7 postscript figure
Satellite holmium M-edge spectra from the magnetic phase via resonant x-ray scattering
Developing an expression of resonant x-ray scattering (RXS) amplitude which
is convenient for investigating the contributions from the higher rank tensor
on the basis of a localized electron picture, we analyze the RXS spectra from
the magnetic phases of Ho near the absorption edges. At the
edge in the uniform helical phase, the calculated spectra of the absorption
coefficient, the RXS intensities at the first and second satellite spots
capture the properties the experimental data possess, such as the spectral
shapes and the peak positions. This demonstrates the plausibility of the
adoption of the localized picture in this material and the effectiveness of the
spectral shape analysis. The latter point is markedly valuable since the
azimuthal angle dependence, which is one of the most useful informations RXS
can provides, is lacking in the experimental conditions. Then, by focusing on
the temperature dependence of the spectral shape at the second satellite spot,
we expect that the spectrum is the contribution of the pure rank two profile in
the uniform helical and the conical phases while that is dominated by the rank
one profile in the intermediate temperature phase, so-called spin slip phase.
The change of the spectral shape as a function of temperature indicates a
direct evidence of the change of magnetic structures undergoing. Furthermore,
we predict that the intensity, which is the same order observed at the second
satellite spot, is expected at the fourth satellite spot from the conical phase
in the electric dipolar transition.Comment: 24 pages, 5 figure
Striking increase in incidence of prostate cancer in men aged < 60 years without improvement in prognosis
Increased awareness and improved diagnostic techniques have led to earlier diagnosis of prostate cancer and increased detection of subclinical cases, resulting in improved prognosis. We postulated that the considerable increase in incidence under age 60 is not attributable only to increased detection. To test this hypothesis, we studied incidence, mortality and relative survival among middle-aged patients diagnosed in south-east Netherlands and East Anglia (UK) between 1971 and 1994. Prostate-specific antigen (PSA) testing did not occur before 1990. Between 1971 and 1989, the age-standardized incidence at ages40–59 increased from 8.8 to 12.5 per 105 in The Netherlands and from 7.0 to 11.6 per 105 in East Anglia.Five-year relative survival did not improve in East Anglia and even declined in south-east Netherlands from 65% [95% confidence interval (CI) 47–83) in 1975–79 to 48% (CI 34–62) in 1985–89. Mortality due to prostate cancer among men aged 45–64 years increased by 50% in south-east Netherlands and by 61% in East Anglia between 1971 and 1989, but decreased slightly in the 1990s. Because other factors adversely influencing the prognosis are unlikely, our results indicate an increase in the incidence of fatal prostate cancer among younger men in the era preceding PSA testing. © 1999 Cancer Research Campaig
Topologically induced confinement of collective modes in multilayer graphene nanocones measured by momentum-resolved STEM-VEELS
Is DRE essential for the follow up of prostate cancer patients? A prospective audit of 194 patients
BACKGROUND: Prostate cancer follow up forms a substantial part of the urology outpatient workload. Nurse led prostate cancer follow up clinics are becoming more common. Routine follow-up may involve performing DRE, which may require training. OBJECTIVES: The aim of this audit was to assess the factors that influenced the change in the management of prostate cancer patients during follow up. This would allow us to pave the way towards a protocol driven follow up clinic led by nurse specialists without formal training in DRE. RESULTS: 194 prostate cancer patients were seen over a period of two months and all the patients had DRE performed on at least one occasion. The management was changed in 47 patients. The most common factor influencing this change was PSA trend. A change in DRE findings influenced advancement of the clinic visit in 2 patients. CONCLUSIONS: PSA is the most common factor influencing change in the management of these patients. Nurse specialists can run prostate cancer follow-up clinics in parallel to existing consultant clinics and reserve DRE only for those patients who have a PSA change or have onset of new symptoms. However larger studies are required involving all the subgroups of patients to identify the subgroups of patients who will require DRE routinely
Nonperturbative renormalization group approach to frustrated magnets
This article is devoted to the study of the critical properties of classical
XY and Heisenberg frustrated magnets in three dimensions. We first analyze the
experimental and numerical situations. We show that the unusual behaviors
encountered in these systems, typically nonuniversal scaling, are hardly
compatible with the hypothesis of a second order phase transition. We then
review the various perturbative and early nonperturbative approaches used to
investigate these systems. We argue that none of them provides a completely
satisfactory description of the three-dimensional critical behavior. We then
recall the principles of the nonperturbative approach - the effective average
action method - that we have used to investigate the physics of frustrated
magnets. First, we recall the treatment of the unfrustrated - O(N) - case with
this method. This allows to introduce its technical aspects. Then, we show how
this method unables to clarify most of the problems encountered in the previous
theoretical descriptions of frustrated magnets. Firstly, we get an explanation
of the long-standing mismatch between different perturbative approaches which
consists in a nonperturbative mechanism of annihilation of fixed points between
two and three dimensions. Secondly, we get a coherent picture of the physics of
frustrated magnets in qualitative and (semi-) quantitative agreement with the
numerical and experimental results. The central feature that emerges from our
approach is the existence of scaling behaviors without fixed or pseudo-fixed
point and that relies on a slowing-down of the renormalization group flow in a
whole region in the coupling constants space. This phenomenon allows to explain
the occurence of generic weak first order behaviors and to understand the
absence of universality in the critical behavior of frustrated magnets.Comment: 58 pages, 15 PS figure
Follow-up care for men with prostate cancer and the role of primary care: a systematic review of international guidelines
The optimal role for primary care in providing follow-up for men with prostate cancer is uncertain. A systematic review of international guidelines was undertaken to help identify key elements of existing models of follow-up care to establish a theoretical basis for evaluating future complex interventions. Many guidelines provide insufficient information to judge the reliability of the recommendations. Although the PSA test remains the cornerstone of follow-up, the diversity of recommendations on the provision of follow-up care reflects the current lack of research evidence on which to base firm conclusions. The review highlights the importance of transparent guideline development procedures and the need for robust primary research to inform future evidence-based models of follow-up care for men with prostate cancer
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