13,301 research outputs found
Radial convection of finite ion temperature, high amplitude plasma blobs
We present results from simulations of seeded blob convection in the
scrape-off-layer of magnetically confined fusion plasmas. We consistently
incorporate high fluctuation amplitude levels and finite Larmor radius (FLR)
effects using a fully nonlinear global gyrofluid model. This is in line with
conditions found in tokamak scrape-off-layers (SOL) regions.
Varying the ion temperature, the initial blob width, and the initial
amplitude, we found an FLR dominated regime where the blob behavior is
significantly different from what is predicted by cold-ion models. The
transition to this regime is very well described by the ratio of the ion
gyroradius to the characteristic gradient scale length of the blob.
We compare the global gyrofluid model with a partly linearized local model.
For low ion temperatures we find that simulations of the global model show more
coherent blobs with an increased cross-field transport compared to blobs
simulated with the local model. The maximal blob amplitude is significantly
higher in the global simulations than in the local ones. When the ion
temperature is comparable to the electron temperature, global blob simulations
show a reduced blob coherence and a decreased cross-field transport in
comparison with local blob simulations
The influence of temperature dynamics and dynamic finite ion Larmor radius effects on seeded high amplitude plasma blobs
Thermal effects on the perpendicular convection of seeded pressure blobs in
the scrape-off layer of magnetised fusion plasmas are investigated. Our
numerical study is based on a four field full-F gyrofluid model, which entails
the consistent description of high fluctuation amplitudes and dynamic finite
Larmor radius effects. We find that the maximal radial blob velocity increases
with the square root of the initial pressure perturbation and that a finite
Larmor radius contributes to highly compact blob structures that propagate in
the poloidal direction. An extensive parameter study reveals that a smooth
transition to this compact blob regime occurs when the finite Larmor radius
effect strength, defined by the ratio of the magnetic field aligned component
of the ion diamagnetic to the vorticity, exceeds unity.
The maximal radial blob velocities agree excellently with the inertial velocity
scaling law over more than an order of magnitude. We show that the finite
Larmor radius effect strength affects the poloidal and total particle transport
and present an empirical scaling law for the poloidal and total blob
velocities. Distinctions to the blob behaviour in the isothermal limit with
constant finite Larmor radius effects are highlighted
Observation of force-detected nuclear magnetic resonance in a homogeneous field
We report the experimental realization of BOOMERANG (better observation of magnetization, enhanced resolution, and no gradient), a sensitive and general method of magnetic resonance. The prototype millimeter-scale NMR spectrometer shows signal and noise levels in agreement with the design principles. We present H-1 and F-19 NMR in both solid and liquid samples, including time-domain Fourier transform NMR spectroscopy, multiple-pulse echoes, and heteronuclear J spectroscopy. By measuring a H-1-F-19 J coupling, this last experiment accomplishes chemically specific spectroscopy with force-detected NMR. In BOOMERANG, an assembly of permanent magnets provides a homogeneous field throughout the sample, while a harmonically suspended part of the assembly, a detector, is mechanically driven by spin-dependent forces. By placing the sample in a homogeneous field, signal dephasing by diffusion in a field gradient is made negligible, enabling application to liquids, in contrast to other force-detection methods. The design appears readily scalable to µm-scale samples where it should have sensitivity advantages over inductive detection with microcoils and where it holds great promise for application of magnetic resonance in biology, chemistry, physics, and surface science. We briefly discuss extensions of the BOOMERANG method to the µm and nm scales
Classification of String-like Solutions in Dilaton Gravity
The static string-like solutions of the Abelian Higgs model coupled to
dilaton gravity are analyzed and compared to the non-dilatonic case. Except for
a special coupling between the Higgs Lagrangian and the dilaton, the solutions
are flux tubes that generate a non-asymptotically flat geometry. Any point in
parameter space corresponds to two branches of solutions with two different
asymptotic behaviors. Unlike the non-dilatonic case, where one branch is always
asymptotically conic, in the present case the asymptotic behavior changes
continuously along each branch.Comment: 15 pages, 6 figures. To be published in Phys. Rev.
Colour-singlet strangelets at finite temperature
Considering massless and quarks, and massive (150 MeV) quarks in
a bag with the bag pressure constant MeV, a colour-singlet
grand canonical partition function is constructed for temperatures
MeV. Then the stability of finite size strangelets is studied minimizing the
free energy as a function of the radius of the bag. The colour-singlet
restriction has several profound effects when compared to colour unprojected
case: (1) Now bulk energy per baryon is increased by about MeV making the
strange quark matter unbound. (2) The shell structures are more pronounced
(deeper). (3) Positions of the shell closure are shifted to lower -values,
the first deepest one occuring at , famous -particle ! (4) The shell
structure at vanishes only at MeV, though for higher
-values it happens so at MeV.Comment: Revtex file(8 pages)+6 figures(ps files) available on request from
first Autho
Evanescent single-molecule biosensing with quantum limited precision
Sensors that are able to detect and track single unlabelled biomolecules are
an important tool both to understand biomolecular dynamics and interactions at
nanoscale, and for medical diagnostics operating at their ultimate detection
limits. Recently, exceptional sensitivity has been achieved using the strongly
enhanced evanescent fields provided by optical microcavities and nano-sized
plasmonic resonators. However, at high field intensities photodamage to the
biological specimen becomes increasingly problematic. Here, we introduce an
optical nanofibre based evanescent biosensor that operates at the fundamental
precision limit introduced by quantisation of light. This allows a four
order-of-magnitude reduction in optical intensity whilst maintaining
state-of-the-art sensitivity. It enable quantum noise limited tracking of
single biomolecules as small as 3.5 nm, and surface-molecule interactions to be
monitored over extended periods. By achieving quantum noise limited precision,
our approach provides a pathway towards quantum-enhanced single-molecule
biosensors.Comment: 17 pages, 4 figures, supplementary informatio
Panel Discussion - Management of Eurasian watermilfoil in the United States using native insects: State regulatory and management issues
While researchers have evaluated the potential of native
insect herbivores to manage nonindigenous aquatic plant
species such as Eurasian watermilfoil (
Myriophyllum spicatum
L.), the practical matters of regulatory compliance and implementation
have been neglected. A panel of aquatic nuisance
species program managers from three state natural
resource management agencies (Minnesota, Vermont and
Washington) discussed their regulatory and policy concerns.
In addition, one ecological consultant attempting to market
one of the native insects to manage Eurasian watermilfoil
added his perspective on the special challenges of distributing
a native biological control agent for management of Eurasian
watermilfoil
Magnetoresistence engineering and singlet/triplet switching in InAs nanowire quantum dots with ferromagnetic sidegates
We present magnetoresistance (MR) experiments on an InAs nanowire quantum dot
device with two ferromagnetic sidegates (FSGs) in a split-gate geometry. The
wire segment can be electrically tuned to a single dot or to a double dot
regime using the FSGs and a backgate. In both regimes we find a strong MR and a
sharp MR switching of up to 25\% at the field at which the magnetizations of
the FSGs are inverted by the external field. The sign and amplitude of the MR
and the MR switching can both be tuned electrically by the FSGs. In a double
dot regime close to pinch-off we find {\it two} sharp transitions in the
conductance, reminiscent of tunneling MR (TMR) between two ferromagnetic
contacts, with one transition near zero and one at the FSG switching fields.
These surprisingly rich characteristics we explain in several simple resonant
tunneling models. For example, the TMR-like MR can be understood as a
stray-field controlled transition between singlet and a triplet double dot
states. Such local magnetic fields are the key elements in various proposals to
engineer novel states of matter and may be used for testing electron spin-based
Bell inequalities.Comment: 7 pages, 6 figure
Planar Ion Trap Geometry for Microfabrication
We describe a novel high aspect ratio radiofrequency linear ion trap geometry
that is amenable to modern microfabrication techniques. The ion trap electrode
structure consists of a pair of stacked conducting cantilevers resulting in
confining fields that take the form of fringe fields from parallel plate
capacitors. The confining potentials are modeled both analytically and
numerically. This ion trap geometry may form the basis for large scale quantum
computers or parallel quadrupole mass spectrometers.
PACS: 39.25.+k, 03.67.Lx, 07.75.+h, 07.10+CmComment: 14 pages, 16 figure
- …