2,205 research outputs found
Tuning nonlinearity, dynamic range, and frequency of nanomechanical resonators
We explore an electrostatic mechanism for tuning the nonlinearity of nanomechanical resonators and increasing their dynamic range for sensor applications. We also demonstrate tuning the resonant frequency of resonators both upward and downward. A theoretical model is developed that qualitatively explains the experimental results and serves as a simple guide for design of tunable nanomechanical devices
Dynamic range of nanotube- and nanowire-based electromechanical systems
Nanomechanical resonators with high aspect ratio, such as nanotubes and nanowires are of interest due to their expected high sensitivity. However, a strongly nonlinear response combined with a high thermomechanical noise level limits the useful linear dynamic range of this type of device. We derive the equations governing this behavior and find a strong dependence [[proportional]dsqrt((d/L)[sup 5])] of the dynamic range on aspect ratio
Basins of attraction of a nonlinear nanomechanical resonator
We present an experiment that systematically probes the basins of attraction
of two fixed points of a nonlinear nanomechanical resonator and maps them out
with high resolution. We observe a separatrix which progressively alters shape
for varying drive strength and changes the relative areas of the two basins of
attraction. The observed separatrix is blurred due to ambient fluctuations,
including residual noise in the drive system, which cause uncertainty in the
preparation of an initial state close to the separatrix. We find a good
agreement between the experimentally mapped and theoretically calculated basins
of attraction
Spin effects in transport through non-Fermi liquid quantum dots
The current-voltage characteristic of a one dimensional quantum dot connected
via tunnel barriers to interacting leads is calculated in the region of
sequential tunneling. The spin of the electrons is taken into account.
Non-Fermi liquid correlations implying spin-charge separation are assumed to be
present in the dot and in the leads. It is found that the energetic distance of
the peaks in the linear conductance shows a spin-induced parity effect at zero
temperature T. The temperature dependence of the positions of the peaks depends
on the non-Fermi liquid nature of the system. For non-symmetric tunnel barriers
negative differential conductances are predicted, which are related to the
participation in the transport of collective states in the quantum dot with
larger spins. Without spin-charge separation the negative differential
conductances do not occur. Taking into account spin relaxation destroys the
spin-induced conductance features. The possibility of observing in experiment
the predicted effects are briefly discussed.Comment: 15 pages, 16 figures, accepted for publication on Physical Review
Technical Note: Mesocosm approach to quantify dissolved inorganic carbon percolation fluxes
Dissolved inorganic carbon (DIC) fluxes across the vadose zone are
influenced by a complex interplay of biological, chemical and physical
factors. A novel soil mesocosm system was evaluated as a tool for providing
information on the mechanisms behind DIC percolation to the groundwater from
unplanted soil. Carbon dioxide partial pressure (<i>p</i>CO<sub>2</sub>), alkalinity, soil
moisture and temperature were measured with depth and time, and DIC in the
percolate was quantified using a sodium hydroxide trap. Results showed good
reproducibility between two replicate mesocosms. The <i>p</i>CO<sub>2</sub> varied between
0.2 and 1.1%, and the alkalinity was 0.1–0.6 meq L<sup>−1</sup>. The measured cumulative
effluent DIC flux over the 78-day experimental period was 185–196 mg L<sup>−1</sup> m<sup>−2</sup> and in the same range as estimates derived from
<i>p</i>CO<sub>2</sub> and alkalinity in samples extracted from the side of the mesocosm
column and the drainage flux. Our results indicate that the mesocosm system
is a promising tool for studying DIC percolation fluxes and other
biogeochemical transport processes in unsaturated environments
Neutron Resonance Spectroscopy of 106Pd, and 108Pd from 20–2000 eV
Parity nonconserving asymmetries have been measured in p-wave resonances of 106Pd and 108Pd. The data analysis requires knowledge of the neutron resonance parameters. Transmission and capture γ-ray yields were measured for En=20–2000 eV with the time-of-flight method at the Los Alamos Neutron Science Center (LANSCE). A total of 28 resonances in 106Pd and 32 resonances in 108Pd were studied. The resonance parameters for 106Pd are new for all except one resonance. In 108Pd six new resonances were observed and the precision improved for many of the resonance parameters. A Bayesian analysis was used to assign orbital angular momentum for the resonances studied
Parity Nonconservation in 106Pd and 108Pd Neutron Resonances
Parity nonconservation (PNC) has been studied in the neutron p-wave resonances of 106Pd and 108Pd in the energy range of 20 to 2000 eV. Longitudinal asymmetries in p-wave capture cross sections are measured using longitudinally polarized neutrons incident on ∼20-g metal-powder targets at LANSCE. A CsI γ-ray detector array measures capture cross section asymmetries as a function of neutron energy which is determined by the neutron time-of-flight method. A total of 21 p-wave resonances in 106Pd and 21 p-wave resonances in 108Pd were studied. One statistically significant PNC effect was observed in106Pd, and no effects were observed in 108Pd. For 106Pd a weak spreading width of Γw=34-28+47×10-7 eV was obtained. For 108Pd an upper limit on the weak spreading width of Γw\u3c12×10-7 eV was determined at the 68% confidence level
Pre-eclampsia Diagnosis and Treatment Options:A Review of Published Economic Assessments
Pre-eclampsia is a pregnancy complication affecting both mother and fetus. Although there is no proven effective method to prevent pre-eclampsia, early identification of women at risk of pre-eclampsia could enhance appropriate application of antenatal care, management and treatment. Very little is known about the cost effectiveness of these and other tests for pre-eclampsia, mainly because there is no clear treatment path. The aim of this study was to provide a comprehensive overview of the existing evidence on the health economics of screening, diagnosis and treatment options in pre-eclampsia.We searched three electronic databases (PubMed, EMBASE and the Cochrane Library) for studies on screening, diagnosis, treatment or prevention of pre-eclampsia, published between 1994 and 2014. Only full papers written in English containing complete economic assessments in pre-eclampsia were included.From an initial total of 138 references, six papers fulfilled the inclusion criteria. Three studies were on the cost effectiveness of treatment of pre-eclampsia, two of which evaluated magnesium sulphate for prevention of seizures and the third evaluated the cost effectiveness of induction of labour versus expectant monitoring. The other three studies were aimed at screening and diagnosis, in combination with subsequent preventive measures. The two studies on magnesium sulphate were equivocal on the cost effectiveness in non-severe cases, and the other study suggested that induction of labour in term pre-eclampsia was more cost effective than expectant monitoring. The screening studies were quite diverse in their objectives as well as in their conclusions. One study concluded that screening is probably not worthwhile, while two other studies stated that in certain scenarios it may be cost effective to screen all pregnant women and prophylactically treat those who are found to be at high risk of developing pre-eclampsia.This study is the first to provide a comprehensive overview on the economic aspects of pre-eclampsia in its broadest sense, ranging from screening to treatment options. The main limitation of the present study lies in the variety of topics in combination with the limited number of papers that could be included; this restricted the comparisons that could be made. In conclusion, novel biomarkers in screening for and diagnosing pre-eclampsia show promise, but their accuracy is a major driver of cost effectiveness, as is prevalence. Universal screening for pre-eclampsia, using a biomarker, will be feasible only when accuracy is significantly increased.</p
Quantized Adiabatic Charge Transport in a Carbon Nanotube
The coupling of a metallic Carbon nanotube to a surface acoustic wave (SAW)
is proposed as a vehicle to realize quantized adiabatic charge transport in a
Luttinger liquid system. We demonstrate that electron backscattering by a
periodic SAW potential, which results in miniband formation, can be achieved at
energies near the Fermi level. Electron interaction, treated in a Luttinger
liquid framework, is shown to enhance minigaps and thereby improve current
quantization. Quantized SAW induced current, as a function of electron density,
changes sign at half-filling.Comment: 5 pages, 2 figure
Parity Violation in Neutron Resonances in 107,109Ag
Parity nonconservation (PNC) was studied in p-wave resonances in Ag by measuring the helicity dependence of the neutron total cross section. Transmission measurements on natural Ag were performed in the energy range 32 to 422 eV with the time-of-flight method at the Manuel Lujan Neutron Scattering Center at Los Alamos National Laboratory. A total of 15 p-wave neutron resonances were studied in 107Ag and ninep-wave resonances in 109Ag. Statistically significant asymmetries were observed for eight resonances in 107Ag and for four resonances in109Ag. An analysis treating the PNC matrix elements as random variables yields a weak spreading width of Γw=(2.67-1.21+2.65)×10-7 eV for107Ag and Γw=(1.30-0.74+2.49)×10-7 eV for 109Ag
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