3,327 research outputs found
Non-equilibrium Phase-Ordering with a Global Conservation Law
In all dimensions, infinite-range Kawasaki spin exchange in a quenched Ising
model leads to an asymptotic length-scale
at because the kinetic coefficient is renormalized by the broken-bond
density, . For , activated kinetics recovers the
standard asymptotic growth-law, . However, at all temperatures,
infinite-range energy-transport is allowed by the spin-exchange dynamics. A
better implementation of global conservation, the microcanonical Creutz
algorithm, is well behaved and exhibits the standard non-conserved growth law,
, at all temperatures.Comment: 2 pages and 2 figures, uses epsf.st
Dynamical Stability of Imaged Planetary Systems in Formation: Application to HL Tau
A recent ALMA image revealed several concentric gaps in the protoplanetary
disk surrounding the young star HL Tau. We consider the hypothesis that these
gaps are carved by planets, and present a general framework for understanding
the dynamical stability of such systems over typical disk lifetimes, providing
estimates for the maximum planetary masses. We collect these easily evaluated
constraints into a workflow that can help guide the design and interpretation
of new observational campaigns and numerical simulations of gap opening in such
systems. We argue that the locations of resonances should be significantly
shifted in massive disks like HL Tau, and that theoretical uncertainties in the
exact offset, together with observational errors, imply a large uncertainty in
the dynamical state and stability in such disks. This presents an important
barrier to using systems like HL Tau as a proxy for the initial conditions
following planet formation. An important observational avenue to breaking this
degeneracy is to search for eccentric gaps, which could implicate resonantly
interacting planets. Unfortunately, massive disks like HL Tau should induce
swift pericenter precession that would smear out any such eccentric features of
planetary origin. This motivates pushing toward more typical, less massive
disks. For a nominal non-resonant model of the HL Tau system with five planets,
we find a maximum mass for the outer three bodies of approximately 2 Neptune
masses. In a resonant configuration, these planets can reach at least the mass
of Saturn. The inner two planets' masses are unconstrained by dynamical
stability arguments.Comment: Accepted in ApJ. 16 pages 8 figure
Numerical Simulation of Nano Scanning in Intermittent-Contact Mode AFM under Q control
We investigate nano scanning in tapping mode atomic force microscopy (AFM)
under quality (Q) control via numerical simulations performed in SIMULINK. We
focus on the simulation of whole scan process rather than the simulation of
cantilever dynamics and the force interactions between the probe tip and the
surface alone, as in most of the earlier numerical studies. This enables us to
quantify the scan performance under Q control for different scan settings.
Using the numerical simulations, we first investigate the effect of elastic
modulus of sample (relative to the substrate surface) and probe stiffness on
the scan results. Our numerical simulations show that scanning in attractive
regime using soft cantilevers with high Qeff results in a better image quality.
We, then demonstrate the trade-off in setting the effective Q factor (Qeff) of
the probe in Q control: low values of Qeff cause an increase in tapping forces
while higher ones limit the maximum achievable scan speed due to the slow
response of the cantilever to the rapid changes in surface profile. Finally, we
show that it is possible to achieve higher scan speeds without causing an
increase in the tapping forces using adaptive Q control (AQC), in which the Q
factor of the probe is changed instantaneously depending on the magnitude of
the error signal in oscillation amplitude. The scan performance of AQC is
quantitatively compared to that of standard Q control using iso-error curves
obtained from numerical simulations first and then the results are validated
through scan experiments performed using a physical set-up
Comment on ``Theory of Spinodal Decomposition''
I comment on a paper by S. B. Goryachev [PRL vol 72, p.1850 (1994)] that
presents a theory of non-equilibrium dynamics for scalar systems quenched into
an ordered phase. Goryachev incorrectly applies only a global conservation
constraint to systems with local conservation laws.Comment: 2 pages LATeX (REVTeX macros), no figures. REVISIONS --- more to the
point. microscopic example added, presentation streamlined, long-range
interactions mentioned, to be published in Phys. Rev. Let
Low-noise polymeric nanomechanical biosensors
A sensor device based on a single polymer cantilever and optical readout has been developed for detection of molecular recognition reactions without the need of a reference cantilever for subtraction of unspecific signals. Microcantilevers have been fabricated in the photoresist SU-8 with one surface passivated with a thin fluorocarbon layer. The SU-8 surface is sensitized with biological receptors by applying silanization methods, whereas the fluorocarbon surface remains inert to these processes. The thermal and mechanical properties of the chosen materials allow overcoming the main limitations of gold-coated silicon cantilevers: the temperature, pH, and ionic strength cross sensitivities. This is demonstrated by comparing the response of SU-8 cantilevers and that of gold-coated silicon nitride cantilevers to variations in temperature and pH. The sensitivity of the developed polymeric nanomechanical sensor is demonstrated by real-time detection of the human growth hormone with sensitivity in differential surface stress of about 1 mN/m.The authors acknowledge J. M. Rodríguez-Prado and M. Mellado for providing reagents for the molecular recognition experiments and J. Treviño, E. Mauriz, and D. Haefliger for fruitful discussion. J.T. and M.C. acknowledge financial support from the Spanish Ministry of Science (MERG-CT-2004-
510638) and the European Union (GEN2001-4856-C13-11).Peer reviewe
Isquemia aguda de miembros inferiores secundaria a ergortismo
Paciente de género femenino, de 21 años de edad, quien ingresó por dolor progresivo e intenso en miembros inferiores, y refirió antecedente reciente de ingestión de derivados del ergot. Al examen físico se observó ausencia de pulsos en ambos miembros inferiores. Por angiotomografia se documentó disminución severa, generalizada y bilateral, del calibre de los vasos arteriales de miembros inferiores. Se diagnosticó isquemia arterial aguda secundaria a ergotismo y se inició tratamiento con vasodilatadores y calcio-antagonistas, que resolvió los síntomas en su totalidad.21 years old female patient admitted for progressive and intense pain in lower limbs, that narrated a recent history of ergot ingestion. On physical examination there was absence of pulses in both lower limbs. Severe, generalized and bilateral decrease of caliber of arterial vessels of the lower limbs was documented by angiotomography. Acute arterial ischemia of lower limbs secondary to ergotism was diagnosed and treatment with vasodilators and calcium antagonists was initiated, resolving entirely the symptoms
- …