8,370 research outputs found
Controlling surface morphologies by time-delayed feedback
We propose a new method to control the roughness of a growing surface, via a
time-delayed feedback scheme. As an illustration, we apply this method to the
Kardar-Parisi-Zhang equation in 1+1 dimensions and show that the effective
growth exponent of the surface width can be stabilized at any desired value in
the interval [0.25,0.33], for a significant length of time. The method is quite
general and can be applied to a wide range of growth phenomena. A possible
experimental realization is suggested.Comment: 4 pages, 3 figure
Effect of a pre-milking teat foam and a liner disinfectant on the presence of mesophilic and (proteolytic) psychrotrophic bacteria prior to milking
Contamination of raw milk by psychrotrophs can lead to the production of heat-resistant proteases and subsequent spoilage of UHT milk. Therefore, this research communication evaluated the effect of a pre-milking teat disinfectant (active components: L-(+)-lactic acid and salicylic acid) and a liner disinfectant (active components: peracetic acid and hydrogen peroxide) on the number of mesophilic and (proteolytic) psychrotrophic bacteria prior to milking. The teat orifices of 10 cows were sampled using a swabbing procedure before and after treatment with a pre-milking teat disinfectant on six subsequent days. On the teat orifices, there was a small but statistically significant decrease in the psychrotrophic bacterial counts between pre and post dipping. No differences were observed for the mesophilic bacterial counts and proteolytic active counts. Liners were also sampled using swabs pre and post disinfection. No statistically significant decrease in the bacterial counts was observed post liner disinfection, although there was a numerical decrease. Sixty-two percent of the proteolytic psychrotrophs were pseudomonads: 16.5% of which were P. fragi, 14.3% P. lundensis, 10.0% P. fluorescens and 2.9% P. putida. Trinitrobenzenesulfonic acid (TNBS) analysis revealed a wide variety in proteolytic activity (from 0 to 55 mu mol glycine/ml milk) and the presence of high producers. It can be concluded that there was only a minor effect of teat and liner disinfection on the psychrotrophic bacterial counts indicating that the measures presented did not result in a reduction of the targeted bacteria on teat orifices and liners
Utilization of CT scanning associated with complex spine surgery.
BackgroundDue to the risk associated with exposure to ionizing radiation, there is an urgent need to identify areas of CT scanning overutilization. While increased use of diagnostic spinal imaging has been documented, no previous research has estimated the magnitude of follow-up imaging used to evaluate the postoperative spine.MethodsThis retrospective cohort study quantifies the association between spinal surgery and CT utilization. An insurance database (Humana, Inc.) with ≈ 19 million enrollees was employed, representing 8 consecutive years (2007-2014). Surgical and imaging procedures were captured by anatomic-specific CPT codes. Complex surgeries included all cervical, thoracic and lumbar instrumented spine fusions. Simple surgeries included discectomy and laminectomy. Imaging was restricted to CT and MRI. Postoperative imaging frequency extended to 5-years post-surgery.ResultsThere were 140,660 complex spinal procedures and 39,943 discectomies and 49,889 laminectomies. MRI was the predominate preoperative imaging modality for all surgical procedures (median: 80%; range: 73-82%). Postoperatively, CT prevalence following complex procedures increased more than two-fold from 6 months (18%) to 5 years (≥40%), and patients having a postoperative CT averaged two scans. For simple procedures, the prevalence of postoperative CT scanning never exceeded 30%.ConclusionsCT scanning is used frequently for follow-up imaging evaluation following complex spine surgery. There is emerging evidence of an increased cancer risk due to ionizing radiation exposure with CT. In the setting of complex spine surgery, actions to mitigate this risk should be considered and include reducing nonessential scans, using the lowest possible radiation dose protocols, exerting greater selectivity in monitoring the developing fusion construct, and adopting non-ferromagnetic implant biomaterials that facilitate MRI postoperatively
New limits on "odderon" amplitudes from analyticity constraints
In studies of high energy and scattering, the odd (under
crossing) forward scattering amplitude accounts for the difference between the
and cross sections. Typically, it is taken as
(),
which has as , where is the
ratio of the real to the imaginary portion of the forward scattering amplitude.
However, the odd-signatured amplitude can have in principle a strikingly
different behavior, ranging from having non-zero constant to
having as , the maximal behavior
allowed by analyticity and the Froissart bound. We reanalyze high energy
and scattering data, using new analyticity constraints, in order to
put new and precise limits on the magnitude of ``odderon'' amplitudes.Comment: 13 pages LaTex, 6 figure
A Dust-Penetrated Classification Scheme for Bars as Inferred from their Gravitational Force Fields
The division of galaxies into ``barred'' (SB) and ``normal'' (S) spirals is a
fundamental aspect of the Hubble galaxy classification system. This ``tuning
fork'' view was revised by de Vaucouleurs, whose classification volume
recognized apparent ``bar strength'' (SA, SAB, SB) as a continuous property of
galaxies called the ``family''. However, the SA, SAB, and SB families are
purely visual judgments that can have little bearing on the actual bar strength
in a given galaxy. Until very recently, published bar judgments were based
exclusively on blue light images, where internal extinction or star formation
can either mask a bar completely or give the false impression of a bar in a
nonbarred galaxy. Near-infrared camera arrays, which principally trace the old
stellar populations in both normal and barred galaxies, now facilitate a
quantification of bar strength in terms of their gravitational potentials and
force fields. In this paper, we show that the maximum value, Qb, of the ratio
of the tangential force to the mean radial force is a quantitative measure of
the strength of a bar. Qb does not measure bar ellipticity or bar shape, but
rather depends on the actual forcing due to the bar embedded in its disk. We
show that a wide range of true bar strengths characterizes the category ``SB'',
while de Vaucouleurs category ``SAB'' corresponds to a much narrower range of
bar strengths. We present Qb values for 36 galaxies, and we incorporate our bar
classes into a dust-penetrated classification system for spiral galaxies.Comment: Accepted for publication in the Astrophysical Journal (LaTex, 30
pages + 3 figures); Figs. 1 and 3 are in color and are also available at
http://bama.ua.edu/~rbuta/bars
New physics, the cosmic ray spectrum knee, and cross section measurements
We explore the possibility that a new physics interaction can provide an
explanation for the knee just above GeV in the cosmic ray spectrum. We
model the new physics modifications to the total proton-proton cross section
with an incoherent term that allows for missing energy above the scale of new
physics. We add the constraint that the new physics must also be consistent
with published cross section measurements, using cosmic ray observations,
an order of magnitude and more above the knee. We find that the rise in cross
section required at energies above the knee is radical. The increase in cross
section suggests that it may be more appropriate to treat the scattering
process in the black disc limit at such high energies. In this case there may
be no clean separation between the standard model and new physics contributions
to the total cross section. We model the missing energy in this limit and find
a good fit to the Tibet III cosmic ray flux data. We comment on testing the new
physics proposal for the cosmic ray knee at the Large Hadron Collider.Comment: 17 pages, 4 figure
Self-Consistent Response of a Galactic Disk to an Elliptical Perturbation Halo Potential
We calculate the self-consistent response of an axisymmetric galactic disk
perturbed by an elliptical halo potential of harmonic number m = 2, and obtain
the net disk ellipticity. Such a potential is commonly expected to arise due to
a galactic tidal encounter and also during the galaxy formation process. The
self-gravitational potential corresponding to the self-consistent,
non-axisymmetric density response of the disk is obtained by inversion of
Poisson equation for a thin disk. This response potential is shown to oppose
the perturbation potential, because physically the disk self-gravity resists
the imposed potential. This results in a reduction in the net ellipticity of
the perturbation halo potential in the disk plane. The reduction factor
denoting this decrease is independent of the strength of the perturbation
potential, and has a typical minimum value of 0.75 - 0.9 for a wide range of
galaxy parameters. The reduction is negligible at all radii for higher
harmonics (m > or = 3) of the halo potential. (abridged).Comment: 26 pages (LaTex- aastex style), 3 .eps figures. To appear in the
Astrophysical Journal, Vol. 542, Oct. 20, 200
Low frequency m=1 normal mode oscillations of a self-gravitating disc
A continuous system such as a galactic disc is shown to be well approximated
by an N-ring differentially rotating self-gravitating system. Lowest order
(m=1) non-axisymmetric features such as lopsidedness and warps are global in
nature and quite common in the discs of spiral galaxies. Apparently these two
features of the galactic discs have been treated like two completely disjoint
phenomena. The present analysis based on an eigenvalue approach brings out
clearly that these two features are fundamentally similar in nature and they
are shown to be very Low frequency Normal Mode (LNM) oscillations manifested in
different symmetry planes of the galactic disc. Our analysis also show that
these features are actually long-lived oscillating pattern of the N-ring
self-gravitating system.Comment: 5 figures. Accepted for publication in MNRAS Letter
Small x Behavior of Parton Distributions from the Observed Froissart Energy Dependence of the Deep Inelastic Scattering Cross Section
We fit the reduced cross section for deep-inelastic electron scattering data
to a three parameter ln^2 s fit, A + beta ln^2 (s/s_0), where s= [Q^2/x] (1-x)
+ m^2, and Q^2 is the virtuality of the exchanged photon. Over a wide range in
Q^2 (0.11 < Q^2 < 1200 GeV^2) all of the fits satisfy the logarithmic energy
dependence of the Froissart bound. We can use these results to extrapolate to
very large energies and hence to very small values of Bjorken x -- well beyond
the range accessible experimentally. As Q^2 --> infinity, the structure
function F_2^p(x, Q^2) exhibits Bjorken scaling, within experimental errors. We
obtain new constraints on the behavior of quark and antiquark distribution
functions at small x.Comment: 10 pages, 2 figure
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