649 research outputs found
Taber Vibration Isolator for Vacuum and Cryogenic Applications
We present a procedure for the design and construction of a passive,
multipole, mechanical high-stop vibration isolator. The isolator, consisting of
a stack of metal disks connected by thin wires, attenuates frequencies in the
kilohertz range, and is suited to both vacuum and cryogenic environments. We
derive an approximate analytical model and compare its predictions for the
frequencies of the normal modes to those of a finite element analysis. The
analytical model is exact for the modes involving only motion along and
rotation about the longitudinal axis, and it gives a good approximate
description of the transverse modes. These results show that the high-frequency
behavior of a multi-stage isolator is well characterized by the natural
frequencies of a single stage. From the single-stage frequency formulae, we
derive relationships among the various geometrical parameters of the isolator
to guarantee equal attenuation in all degrees of freedom. We then derive
expressions for the attenuation attainable with a given isolator length, and
find that the most important limiting factor is the elastic limit of the spring
wire material. For our application, which requires attenuations of 250 dB at 1
kHz, our model specifies a six-stage design using brass disks of approximately
2 cm in both radius and thickness, connected by 3 cm steel wires of diameters
ranging from 25 to 75 microns. We describe the construction of this isolator in
detail, and compare measurements of the natural frequencies of a single stage
with calculations from the analytical model and the finite element package. For
translations along and rotations about the longitudinal axes, all three results
are in agreement to within 10% accuracy.Comment: 11 pages, 13 figures, REVTe
Immobilized WNT proteins act as a stem cell niche for tissue engineering
The timing, location, and level of WNT signaling are highly regulated during embryonic development and for the maintenance of adult tissues. Consequently the ability to provide a defined and directed source of WNT proteins is crucial to fully understand its role in tissue development and to mimic its activity in vitro. Here we describe a one-step immobilization technique to covalently bind WNT3A proteins as a basal surface with easy storage and long-lasting activity. We show that this platform is able to maintain adult and embryonic stem cells while also being adaptable for 3D systems. Therefore, this platform could be used for recapitulating specific stem cell niches with the goal of improving tissue engineering
Projected increase in amyotrophic lateral sclerosis from 2015 to 2040
Although amyotrophic lateral sclerosis (ALS) is relatively rare, the socioeconomic significance of the disease is extensive. It is therefore vital to project the epidemiologic trend of ALS. To date, there have been few published studies attempting to estimate the number and distribution of ALS cases in the upcoming years. Here we show that the number of ALS cases across the globe will increase from 222,801 in 2015 to 376,674 in 2040, representing an increase of 69%. This increase is predominantly due to ageing of the population, particularly among developing nations. This projection is likely an underestimate due to improving healthcare and economic conditions. The results should be used to inform healthcare policy to more efficiently allocate healthcare resources
Four new T dwarfs identified in PanSTARRS 1 commissioning data
A complete well-defined sample of ultracool dwarfs is one of the key science
programs of the Pan-STARRS 1 optical survey telescope (PS1). Here we combine
PS1 commissioning data with 2MASS to conduct a proper motion search
(0.1--2.0\arcsec/yr) for nearby T dwarfs, using optical+near-IR colors to
select objects for spectroscopic followup. The addition of sensitive far-red
optical imaging from PS1 enables discovery of nearby ultracool dwarfs that
cannot be identified from 2MASS data alone. We have searched 3700 sq. deg. of
PS1 y-band (0.95--1.03 um) data to y19.5 mag (AB) and J16.5
mag (Vega) and discovered four previously unknown bright T dwarfs. Three of the
objects (with spectral types T1.5, T2 and T3.5) have photometric distances
within 25 pc and were missed by previous 2MASS searches due to more restrictive
color selection criteria. The fourth object (spectral type T4.5) is more
distant than 25 pc and is only a single-band detection in 2MASS. We also
examine the potential for completing the census of nearby ultracool objects
with the PS1 3 survey.Comment: 25 pages, 8 figures, 5 table, AJ accepted, updated to comply with
Pan-STARRS1 naming conventio
A Complete Catalog of Swift GRB Spectra and Durations: Demise of a Physical Origin for Pre-Swift High-Energy Correlations
We calculate durations and spectral paramaters for 218 Swift bursts detected
by the BAT instrument between and including GRBs 041220 and 070509, including
77 events with measured redshifts. Incorporating prior knowledge into the
spectral fits, we are able to measure the characteristic spectral
peak energy and the isotropic equivalent energy
(1-- keV) for all events. This complete and rather extensive catalog,
analyzed with a unified methodology, allows us to address the persistence and
origin of high-energy correlations suggested in pre-Swift observations. We find
that the - correlation is present in the Swift
sample; however, the best-fit powerlaw relation is inconsistent with the
best-fit pre-Swift relation at >5 sigma significance. Moreover, it has a factor
>~ 2 larger intrinsic scatter, after accounting for large errors on . A large fraction of the Swift events are hard and subluminous
relative to (and inconsistent with) the pre-Swift relation, in agreement with
indications from BATSE GRBs without redshift. Moreover, we determine an
experimental threshold for the BAT detector and show how the -- correlation arises artificially due to partial
correlation with the threshold. We show that pre-Swift correlations found by
Amati et al.(2002), Yonetoku et al. (2004), Firmani et al.(2006) (and
independently by others) are likely unrelated to the physical properties of
GRBs and are likely useless for tests of cosmology. Also, an explanation of
these correlations in terms of a detector threshold provides a natural and
quantitative explanation for why short-duration GRBs and events at low redshift
tend to be outliers to the correlations.Comment: 25 pages, 9 figures, 2 tables, Accepted to Ap
New Experimental Limits on Macroscopic Forces Below 100 Microns
Results of an experimental search for new macroscopic forces with Yukawa
range between 5 and 500 microns are presented. The experiment uses 1 kHz
mechanical oscillators as test masses with a stiff conducting shield between
them to suppress backgrounds. No signal is observed above the instrumental
thermal noise after 22 hours of integration time. These results provide the
strongest limits to date between 10 and 100 microns, improve on previous limits
by as much as three orders of magnitude, and rule out half of the remaining
parameter space for predictions of string-inspired models with low-energy
supersymmetry breaking. New forces of four times gravitational strength or
greater are excluded at the 95% confidence level for interaction ranges between
200 and 500 microns.Comment: 25 Pages, 7 Figures: Minor Correction
Single-phonon addition and subtraction to a mechanical thermal state
Adding or subtracting a single quantum of excitation to a thermal state of a bosonic system has the counter-intuitive effect of approximately doubling its mean thermal occupation. We perform the first experimental demonstration of this effect outside optics by implementing single-phonon addition and subtraction to a thermal state of a mechanical oscillator via Brillouin optomechanics in an optical whispering-gallery microresonator. Using a detection scheme that combines single-photon counting and optical heterodyne detection, we observe this doubling of the mechanical thermal fluctuations to a high precision. The capabilities of this joint click-dyne detection scheme adds a significant new dimension for optomechanical quantum science and applications
Single-phonon addition and subtraction to a mechanical thermal state
Adding or subtracting a single quantum of excitation to a thermal state of a
bosonic system has the counter-intuitive effect of approximately doubling its
mean occupation. We perform the first experimental demonstration of this effect
outside optics by implementing single-phonon addition and subtraction to a
thermal state of a mechanical oscillator via Brillouin optomechanics in an
optical whispering-gallery microresonator. Using a detection scheme that
combines single-photon counting and optical heterodyne detection, we observe
this doubling of the mechanical thermal fluctuations to a high precision. The
capabilities of this joint click-dyne detection scheme adds a significant new
dimension for optomechanical quantum science and applications
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