1,347 research outputs found
Nanoladder cantilevers made from diamond and silicon
We present a "nanoladder" geometry that minimizes the mechanical dissipation
of ultrasensitive cantilevers. A nanoladder cantilever consists of a
lithographically patterned scaffold of rails and rungs with feature size
100 nm. Compared to a rectangular beam of the same dimensions, the mass and
spring constant of a nanoladder are each reduced by roughly two orders of
magnitude. We demonstrate a low force noise of zN and zN in a one-Hz bandwidth for devices made from silicon and
diamond, respectively, measured at temperatures between 100--150 mK. As opposed
to bottom-up mechanical resonators like nanowires or nanotubes, nanoladder
cantilevers can be batch-fabricated using standard lithography, which is a
critical factor for applications in scanning force microscopy
Thermal lensing-induced bifocusing of spatial solitons in Kerr-type optical media
Thermo-optical effects cause a bifocusing of incoming beams in optical media,
due to the birefringence created by a thermal lens that can resolve the
incoming beams into two-component signals of different polarizations. We
propose a non-perturbative theoretical description of the process of formation
of double-pulse solitons in Kerr optical media with a thermally-induced
birefringence, based on solving simultaneously the heat equation and the
propagation equation for a beam in a one-dimensional medium with uniform heat
flux load. By means of a non-isospectral Inverse Scattering Transform assuming
an initial solution with a pulse shape, a one-soliton solution to the wave
equation is obtained that represents a double-pulse beam which characteristic
properties depend strongly on the profile of heat spatial distribution.Comment: 5 pages, 2 figure
Sources and distribution of trace species in Alpine precipitation inferred from two 60-year ice core paleorecords
International audienceThe Alps represent the largest barrier to meridional air flow in Europe, strongly influencing the weather and hence the distribution of atmospheric trace components. Here for the first time, chemical records from two ice cores retrieved from glaciers located in the northern and southern Swiss Alps were compared in conjunction with an analysis of "weather type", in order to assess geographical and seasonal trends in the deposition of trace species and to identify source regions and transport patterns. Using a correlation analysis, investigated trace species (NH4+, NO3?, SO42?, Ca2+, Mg2+, Na+, K+, and Cl? were grouped into classes of different origin (anthropogenic, sea salt, or Saharan dust). Over the last 60 years, precipitation chemistry at both sites was dominated by NH4+, NO4?, and SO42?, all of anthropogenic origin and deposited mainly in summer by way of convective precipitation. The similarity of the SO42? profiles with historical records of SO4 emissions from France and Italy indicated these two countries as key source areas for the anthropogenic species. In contrast, sea salt and Saharan dust showed major differences in transport pattern and deposition across the Alps. Currently, the sea-salt constituents Na+, K+, and Cl? are transported to the northern site during advective westerly-wind situations, independent of Saharan dust events. At the southern site, sea salt and Saharan dust are deposited simultaneously, indicating a coupled transport active mainly in summer during south-westerly wind situations
PHP64 Reorganisation of Hospital Emergency Services: A Business Case for Quality Improvement
In Switzerland, emergency care has no gatekeeping system and emergency wards are increasingly overcrowded by walk-in patients. This leads to inefficient use of spezialised resources. Treatment costs are paid by public sources and, beyond some co-payment, reimbursed by health care insurances via tariffs. Given the problems above, a public hospital (Stadtspital Waid; Zurich; catchment population 180'000 people) reorganised its emergency service in 2008. A nurse led triage system and a General Practitioner-led emergency service was implemented beside the conventional emergency ward
Compact Frontend-Electronics and Bidirectional 3.3 Gbps Optical Datalink for Fast Proportional Chamber Readout
The 9600 channels of the multi-wire proportional chamber of the H1 experiment
at HERA have to be read out within 96 ns and made available to the trigger
system. The tight spatial conditions at the rear end flange require a compact
bidirectional readout electronics with minimal power consumption and dead
material.
A solution using 40 identical optical link modules, each transferring the
trigger information with a physical rate of 4 x 832 Mbps via optical fibers,
has been developed and commisioned. The analog pulses from the chamber can be
monitored and the synchronization to the global HERA clock signal is ensured.Comment: 13 pages, 10 figure
Photon angular distribution and nuclear-state alignment in nuclear excitation by electron capture
The alignment of nuclear states resonantly formed in nuclear excitation by
electron capture (NEEC) is studied by means of a density matrix technique. The
vibrational excitations of the nucleus are described by a collective model and
the electrons are treated in a relativistic framework. Formulas for the angular
distribution of photons emitted in the nuclear relaxation are derived. We
present numerical results for alignment parameters and photon angular
distributions for a number of heavy elements in the case of E2 nuclear
transitions. Our results are intended to help future experimental attempts to
discern NEEC from radiative recombination, which is the dominant competing
process
Angular distribution studies on the two-photon ionization of hydrogen-like ions: Relativistic description
The angular distribution of the emitted electrons, following the two-photon
ionization of the hydrogen-like ions, is studied within the framework of second
order perturbation theory and the Dirac equation. Using a density matrix
approach, we have investigated the effects which arise from the polarization of
the incoming light as well as from the higher multipoles in the expansion of
the electron--photon interaction. For medium- and high-Z ions, in particular,
the non-dipole contributions give rise to a significant change in the angular
distribution of the emitted electrons, if compared with the electric-dipole
approximation. This includes a strong forward emission while, in dipole
approxmation, the electron emission always occurs symmetric with respect to the
plane which is perpendicular to the photon beam. Detailed computations for the
dependence of the photoelectron angular distributions on the polarization of
the incident light are carried out for the ionization of H, Xe, and
U (hydrogen-like) ions.Comment: 16 pages, 4 figures, published in J Phys
Bound-bound pair production in relativistic collisions
Electron-positron pair production is considered in the relativistic collision
of a nucleus and an anti-nucleus, in which both leptons are created in bound
states of the corresponding nucleus-lepton system. Compared to free and
bound-free pair production this process is shown to display a qualitatively
different dependency both on the impact energy and charged of the colliding
particles. Interestingly, at high impact energies the cross section for this
process is found to be larger than that for the analogous atomic process of
non-radiative electron capture although the latter does not involve the
creation of new particles.Comment: 4 pages, 3 figure
Ultrasensitive force detection with a nanotube mechanical resonator
Since the advent of atomic force microscopy, mechanical resonators have been
used to study a wide variety of phenomena, such as the dynamics of individual
electron spins, persistent currents in normal metal rings, and the Casimir
force. Key to these experiments is the ability to measure weak forces. Here, we
report on force sensing experiments with a sensitivity of 12 zN Hz^(-1/2) at a
temperature of 1.2 K using a resonator made of a carbon nanotube. An
ultra-sensitive method based on cross-correlated electrical noise measurements,
in combination with parametric downconversion, is used to detect the
low-amplitude vibrations of the nanotube induced by weak forces. The force
sensitivity is quantified by applying a known capacitive force. This detection
method also allows us to measure the Brownian vibrations of the nanotube down
to cryogenic temperatures. Force sensing with nanotube resonators offers new
opportunities for detecting and manipulating individual nuclear spins as well
as for magnetometry measurements.Comment: Early version. To be published in Nature Nanotechnolog
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