6,937 research outputs found
Effective affinities in microarray data
In the past couple of years several studies have shown that hybridization in
Affymetrix DNA microarrays can be rather well understood on the basis of simple
models of physical chemistry. In the majority of the cases a Langmuir isotherm
was used to fit experimental data. Although there is a general consensus about
this approach, some discrepancies between different studies are evident. For
instance, some authors have fitted the hybridization affinities from the
microarray fluorescent intensities, while others used affinities obtained from
melting experiments in solution. The former approach yields fitted affinities
that at first sight are only partially consistent with solution values. In this
paper we show that this discrepancy exists only superficially: a sufficiently
complete model provides effective affinities which are fully consistent with
those fitted to experimental data. This link provides new insight on the
relevant processes underlying the functioning of DNA microarrays.Comment: 8 pages, 6 figure
A generalized experimental investigation of hot gas recirculation and ingestion for jet VTOL aircraft
Jet VTOL aircraft inlet temperature rise and induced recirculating flow pattern
A multifactorial approach for understanding fall risk in older people
OBJECTIVE: To identify the interrelationships and discriminatory value of a broad range of objectively measured explanatory risk factors for falls.
DESIGN: Prospective cohort study with 12-month follow-up period.
SETTING: Community sample.
PARTICIPANTS: Five hundred community-dwelling people aged 70 to 90.
MEASUREMENTS: All participants underwent assessments on medical, disability, physical, cognitive, and psychological measures. Fallers were defined as people who had at least one injurious fall or at least two noninjurious falls during a 12-month follow-up period.
RESULTS: Univariate regression analyses identified the following fall risk factors: disability, poor performance on physical tests, depressive symptoms, poor executive function, concern about falling, and previous falls. Classification and regression tree analysis revealed that balance-related impairments were critical predictors of falls. In those with good balance, disability and exercise levels influenced future fall risk-people in the lowest and the highest exercise tertiles were at greater risk. In those with impaired balance, different risk factors predicted greater fall risk-poor executive function, poor dynamic balance, and low exercise levels. Absolute risks for falls ranged from 11% in those with no risk factors to 54% in the highest-risk group.
CONCLUSIONS: A classification and regression tree approach highlighted interrelationships and discriminatory value of important explanatory fall risk factors. The information may prove useful in clinical settings to assist in tailoring interventions to maximize the potential benefit of falls prevention strategies
VOLTAGE BREAKDOWN IN IONIZED AIR AT FREQUENCIES FROM ZERO TO 10,000 MEGACYCLES
During the summer of 1957, The Martin Company, Denver Division, expressed a need for experimental data which would enable more exact design of surface- mounted antennas on missiles which would avoid corona and voltage breakdown in the higher atmosphere. Inasmuch as some experimental data were then avail* able, a request was also made for a literature search on voltage breakdown is air as a function of pressure, frequency, pulse length, electrode spacing, and degree of ionization. Contract No. DEN 57-5652, under Prime Contract AF 04 (645) 56, was initiated with the Purdue Research Foundation in January, 1958, to obtain (l) a literature search and (2) experimental data covering a range of the parameters listed above. The literature search was delivered to The Martin Company on November 25, 1958. The experimental data are the subject of this report
A tunable macroscopic quantum system based on two fractional vortices
We propose a tunable macroscopic quantum system based on two fractional
vortices. Our analysis shows that two coupled fractional vortices pinned at two
artificially created \kappa\ discontinuities of the Josephson phase in a long
Josephson junction can reach the quantum regime where coherent quantum
oscillations arise. For this purpose we map the dynamics of this system to that
of a single particle in a double-well potential. By tuning the \kappa\
discontinuities with injector currents we are able to control the parameters of
the effective double-well potential as well as to prepare a desired state of
the fractional vortex molecule. The values of the parameters derived from this
model suggest that an experimental realisation of this tunable macroscopic
quantum system is possible with today's technology.Comment: We updated our manuscript due to a change of the focus from qubit to
macroscopic quantum effect
Pattern formation during the evaporation of a colloidal nanoliter drop: a numerical and experimental study
An efficient way to precisely pattern particles on solid surfaces is to
dispense and evaporate colloidal drops, as for bioassays. The dried deposits
often exhibit complex structures exemplified by the coffee ring pattern, where
most particles have accumulated at the periphery of the deposit. In this work,
the formation of deposits during the drying of nanoliter colloidal drops on a
flat substrate is investigated numerically and experimentally. A finite-element
numerical model is developed that solves the Navier-Stokes, heat and mass
transport equations in a Lagrangian framework. The diffusion of vapor in the
atmosphere is solved numerically, providing an exact boundary condition for the
evaporative flux at the droplet-air interface. Laplace stresses and thermal
Marangoni stresses are accounted for. The particle concentration is tracked by
solving a continuum advection-diffusion equation. Wetting line motion and the
interaction of the free surface of the drop with the growing deposit are
modeled based on criteria on wetting angles. Numerical results for evaporation
times and flow field are in very good agreement with published experimental and
theoretical results. We also performed transient visualization experiments of
water and isopropanol drops loaded with polystyrene microsphere evaporating on
respectively glass and polydimethylsiloxane substrates. Measured evaporation
times, deposit shape and sizes, and flow fields are in very good agreement with
the numerical results. Different flow patterns caused by the competition of
Marangoni loops and radial flow are shown to determine the deposit shape to be
either a ring-like pattern or a homogeneous bump
Geometry and symmetries of multi-particle systems
The quantum dynamical evolution of atomic and molecular aggregates, from
their compact to their fragmented states, is parametrized by a single
collective radial parameter. Treating all the remaining particle coordinates in
d dimensions democratically, as a set of angles orthogonal to this collective
radius or by equivalent variables, bypasses all independent-particle
approximations. The invariance of the total kinetic energy under arbitrary
d-dimensional transformations which preserve the radial parameter gives rise to
novel quantum numbers and ladder operators interconnecting its eigenstates at
each value of the radial parameter.
We develop the systematics and technology of this approach, introducing the
relevant mathematics tutorially, by analogy to the familiar theory of angular
momentum in three dimensions. The angular basis functions so obtained are
treated in a manifestly coordinate-free manner, thus serving as a flexible
generalized basis for carrying out detailed studies of wavefunction evolution
in multi-particle systems.Comment: 37 pages, 2 eps figure
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