1,848 research outputs found
A thermostable trilayer resist for niobium lift-off
We have developped a novel lift-off process for fabrication of high quality
superconducting submicron niobium structures. The process makes use of a
thermostable polymer with a high transition temperature T_{g}= 235 C and an
excellent chemical stability. The superconducting critical temperature of 100
nm wide niobium lines is above 7 K. An example of shadow evaporation of a Nb-Cu
submicron hybrid structure is given. A potential application of this process is
the fabrication of very small single electron devices using refratory metals.Comment: 6 pages, 6 eps figures, submitted to Journal of Vacuum Science and
Technology
Walks of molecular motors in two and three dimensions
Molecular motors interacting with cytoskeletal filaments undergo peculiar
random walks consisting of alternating sequences of directed movements along
the filaments and diffusive motion in the surrounding solution. An ensemble of
motors is studied which interacts with a single filament in two and three
dimensions. The time evolution of the probability distribution for the bound
and unbound motors is determined analytically. The diffusion of the motors is
strongly enhanced parallel to the filament. The analytical expressions are in
excellent agreement with the results of Monte Carlo simulations.Comment: 7 pages, 2 figures, to be published in Europhys. Let
Stellar Populations and Mass-Loss in M15: A Spitzer Detection of Dust in the Intra-Cluster Medium
We present Spitzer Space Telescope IRAC and MIPS observations of the galactic
globular cluster M15 (NGC 7078), one of the most metal-poor clusters with a
[Fe/H] = -2.4. Our Spitzer images reveal a population of dusty red giants near
the cluster center, a previously detected planetary nebula (PN) designated
K648, and a possible detection of the intra-cluster medium (ICM) arising from
mass loss episodes from the evolved stellar population. Our analysis suggests 9
(+/-2) x 10^-4 solar masses of dust is present in the core of M15, and this
material has accumulated over a period of approximately 10^6 years, a timescale
ten times shorter than the last galactic plane crossing event. We also present
Spitzer IRS follow up observations of K648, including the detection of the
[NeII] 12.81 micron line, and discuss abundances derived from infrared fine
structure lines.Comment: Accepted for publication in AJ. 20 pages, 10 figures, 6 tables. Full
resolution versions of figures 1, 5, 7, and 8 are available in a PDF version
of this manuscript at http://ir.astro.umn.edu/~mboyer/ms_060906.pd
Controlled interfacial assembly of 2D curved colloidal crystals and jammed shells
Assembly of colloidal particles on fluid interfaces is a promising technique
for synthesizing two-dimensional micro-crystalline materials useful in fields
as diverse as biomedicine1, materials science2, mineral flotation3 and food
processing4. Current approaches rely on bulk emulsification methods, require
further chemical and thermal treatments, and are restrictive with respect to
the materials employed5-9. The development of methods that exploit the great
potential of interfacial assembly for producing tailored materials have been
hampered by the lack of understanding of the assembly process. Here we report a
microfluidic method that allows direct visualization and understanding of the
dynamics of colloidal crystal growth on curved interfaces. The crystals are
periodically ejected to form stable jammed shells, which we refer to as
colloidal armour. We propose that the energetic barriers to interfacial crystal
growth and organization can be overcome by targeted delivery of colloidal
particles through hydrodynamic flows. Our method allows an unprecedented degree
of control over armour composition, size and stability.Comment: 18 pages, 5 figure
High-excitation OH and H_2O lines in Markarian 231: the molecular signatures of compact far-infrared continuum sources
The ISO/LWS far-infrared spectrum of the ultraluminous galaxy Mkn 231 shows
OH and H_2O lines in absorption from energy levels up to 300 K above the ground
state, and emission in the [O I] 63 micron and [C II] 158 micron lines. Our
analysis shows that OH and H_2O are radiatively pumped by the far-infrared
continuum emission of the galaxy. The absorptions in the high-excitation lines
require high far-infrared radiation densities, allowing us to constrain the
properties of the underlying continuum source. The bulk of the far-infrared
continuum arises from a warm (T_dust=70-100 K), optically thick
(tau_100micron=1-2) medium of effective diameter 200-400 pc. In our best-fit
model of total luminosity L_IR, the observed OH and H2O high-lying lines arise
from a luminous (L/L_IR~0.56) region with radius ~100 pc. The high surface
brightness of this component suggests that its infrared emission is dominated
by the AGN. The derived column densities N(OH)>~10^{17} cm^{-2} and
N(H_2O)>~6x10^{16} cm^{-2} may indicate XDR chemistry, although significant
starburst chemistry cannot be ruled out. The lower-lying OH, [C II] 158 micron,
and [O I] 63 micron lines arise from a more extended (~350 pc) starburst
region. We show that the [C II] deficit in Mkn 231 is compatible with a high
average abundance of C+ because of an extreme overall luminosity to gas mass
ratio. Therefore, a [C II] deficit may indicate a significant contribution to
the luminosity by an AGN, and/or by extremely efficient star formation.Comment: 16 pages, 6 figures, accepted for publication in The Astrophysical
Journa
Intra-articular angiolipoma of the knee: a case report
We report a case of intra-articular angiolipoma of the knee. This case report describes our experience in excising an intra-articular angiolipoma of the knee joint. Complete resection under arthroscopy was performed in a 30-year-old man. Two years after the surgery, no evidence of recurrence was seen. Intra-articular angiolipomas should be considered in the differential diagnosis of intra-articular masses in adolescents with recurrent hemarthrosis without trauma
Movement variability in stroke patients and controls performing two upper limb functional tasks: a new assessment methodology
Background: In the evaluation of upper limb impairment post stroke there remains a gap between detailed kinematic analyses with expensive motion capturing systems and common clinical assessment tests. In particular, although many clinical tests evaluate the performance of functional
tasks, metrics to characterise upper limb kinematics are generally not applicable to such tasks and very limited in scope. This paper reports on a novel, user-friendly methodology that allows for the assessment of both signal magnitude and timing variability in upper limb movement trajectories during functional task performance. In order to demonstrate the technique, we report on a study
in which the variability in timing and signal magnitude of data collected during the performance of two functional tasks is compared between a group of subjects with stroke and a group of individually matched control subjects.
Methods: We employ dynamic time warping for curve registration to quantify two aspects of movement variability: 1) variability of the timing of the accelerometer signals' characteristics and 2) variability of the signals' magnitude. Six stroke patients and six matched controls performed several trials of a unilateral ('drinking') and a bilateral ('moving a plate') functional task on two different days, approximately 1 month apart. Group differences for the two variability metrics were investigated on both days.
Results: For 'drinking from a glass' significant group differences were obtained on both days for
the timing variability of the acceleration signals' characteristics (p = 0.002 and p = 0.008 for test and
retest, respectively); all stroke patients showed increased signal timing variability as compared to
their corresponding control subject. 'Moving a plate' provided less distinct group differences.
Conclusion: This initial application establishes that movement variability metrics, as determined
by our methodology, appear different in stroke patients as compared to matched controls during unilateral task performance ('drinking'). Use of a user-friendly, inexpensive accelerometer makes this methodology feasible for routine clinical evaluations. We are encouraged to perform larger studies to further investigate the metrics' usefulness when quantifying levels of impairment
New Low Accretion-Rate Magnetic Binary Systems and their Significance for the Evolution of Cataclysmic Variables
Discoveries of two new white dwarf plus M star binaries with striking optical
cyclotron emission features from the Sloan Digital Sky Survey (SDSS) brings to
six the total number of X-ray faint, magnetic accretion binaries that accrete
at rates < 10^{-13} Msun/yr, or <1% of the values normally encountered in
cataclysmic variables. This fact, coupled with donor stars that underfill their
Roche lobes and very cool white dwarfs, brand the binaries as post
common-envelope systems whose orbits have not yet decayed to the point of
Roche-lobe contact. They are pre-magnetic CVs, or pre-Polars. The systems
exhibit spin/orbit synchronism and apparently accrete by efficient capture of
the stellar wind from the secondary star, a process that has been dubbed a
``magnetic siphon''. Because of this, period evolution of the binaries will
occur solely by gravitational radiation, which is very slow for periods >3 hr.
Optical surveys for the cyclotron harmonics appear to be the only means of
discovery, so the space density of pre-Polars could rival that of Polars, and
the binaries provide an important channel of progenitors (in addition to the
asynchronous Intermediate Polars). Both physical and SDSS observational
selection effects are identified that may help to explain the clumping of all
six systems in a narrow range of magnetic field strength around 60 MG.Comment: 25 pages, 13 figures, Accepted to Ap
Lit up and left dark: Failures of imagination in urban broadband networks
The design and deployment of urban broadband infrastructures inscribe particular imaginations of Internet access onto city streets. The different manifestations and locations of these networks, their uses, and access points often expose material excesses of urban broadband networks, as well as failures of Internet service providers, urban planners, and public officials to imagine the diverse ways that people incorporate Internet connection into their everyday lives. We approach the study of urban broadband networks through the juxtaposition of invisible networks that are buried under the streets and have always been âturned offâ (dark fiber) versus hypervisible that are âturned onâ and prominently displayed on city streets (LinkNYC). In our analysis of these two case studies, we critique themes of visibility and invisibility as indexes of power and access. Our findings are meant to provide a critical analysis of urban technology policy as well as theories of infrastructure, visibility, and access
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