399 research outputs found
Interaction model for magnetic holes in a ferrofluid layer
Nonmagnetic spheres confined in a ferrofluid layer (magnetic holes) present
dipolar interactions when an external magnetic field is exerted. The
interaction potential of a microsphere pair is derived analytically, with a
precise care for the boundary conditions along the glass plates confining the
system. Considering external fields consisting of a constant normal component
and a high frequency rotating in-plane component, this interaction potential is
averaged over time to exhibit the average interparticular forces acting when
the imposed frequency exceeds the inverse of the viscous relaxation time of the
system. The existence of an equilibrium configuration without contact between
the particles is demonstrated for a whole range of exciting fields, and the
equilibrium separation distance depending on the structure of the external
field is established. The stability of the system under out-of-plane buckling
is also studied. The dynamics of such a particle pair is simulated and
validated by experiments.Comment: 15 pages, 11 figures (18 with subfigures). to appear in Phys. Rev.
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
Temperature dependent surface relaxations of Ag(111)
The temperature dependent surface relaxation of Ag(111) is calculated by
density-functional theory. At a given temperature, the equilibrium geometry is
determined by minimizing the Helmholtz free energy within the quasiharmonic
approximation. To this end, phonon dispersions all over the Brillouin zone are
determined from density-functional perturbation theory. We find that the
top-layer relaxation of Ag(111) changes from an inward contraction (-0.8 %) to
an outward expansion (+6.3%) as the temperature increases from T=0 K to 1150 K,
in agreement with experimental findings. Also the calculated surface phonon
dispersion curves at room temperature are in good agreement with helium
scattering measurements. The mechanism driving this surface expansion is
analyzed.Comment: 6 pages, 7 figures, submitted to Phys. Rev. B (May 1998). Other
related publications can be found at
http://www.rz-berlin.mpg.de/th/paper.htm
'If you had only listened carefully...':the discursive construction of emerging leadership in a UK all-women management team
Increasingly, feminist linguistic research has adopted a discursive perspective to learn how women and men 'do' leadership in gendered ways. 'Women' as a social category is made relevant to this study by virtue of the lack of female senior leaders in UK businesses (Sealy and Vinnicombe, 2013). Much previous research has analysed leadership discourse in mixed gender groups, relying on theories that imply comparisons between men and women. Using an Interactional Sociolinguistic approach, this study aims to learn more about how women perform leadership in the absence of men by analysing the spoken interactions of a women-only team who were engaged in a competitive leadership task. The analysis reveals that the women accomplish leadership in multiple and complex ways that defy binary gendered classifications. Nonetheless, there is a distinctive gendered dynamic to the team's interactions which, it is argued, might be disadvantageous to women aspiring to senior positions
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
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
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