2,977 research outputs found
Scaling laws governing stochastic growth and division of single bacterial cells
Uncovering the quantitative laws that govern the growth and division of
single cells remains a major challenge. Using a unique combination of
technologies that yields unprecedented statistical precision, we find that the
sizes of individual Caulobacter crescentus cells increase exponentially in
time. We also establish that they divide upon reaching a critical multiple
(1.8) of their initial sizes, rather than an absolute size. We show
that when the temperature is varied, the growth and division timescales scale
proportionally with each other over the physiological temperature range.
Strikingly, the cell-size and division-time distributions can both be rescaled
by their mean values such that the condition-specific distributions collapse to
universal curves. We account for these observations with a minimal stochastic
model that is based on an autocatalytic cycle. It predicts the scalings, as
well as specific functional forms for the universal curves. Our experimental
and theoretical analysis reveals a simple physical principle governing these
complex biological processes: a single temperature-dependent scale of cellular
time governs the stochastic dynamics of growth and division in balanced growth
conditions.Comment: Text+Supplementar
Compression Molding and Novel Sintering Treatments for Alnico Type-8 Permanent Magnets in Near-Final Shape with Preferred Orientation
Economic uncertainty in the rare earth (RE) permanent magnet marketplace, as well as in an expanding electric drive vehicle market that favors permanent magnet alternating current synchronous drive motors, motivated renewed research in RE-free permanent magnets like âalnico,â an Al-Ni-Co-Fe alloy. Thus, high-pressure, gas-atomized isotropic type-8H pre-alloyed alnico powder was compression molded with a clean burn-out binder to near-final shape and sintered to density \u3e99% of cast alnico 8 (full density of 7.3 g/cm3). To produce aligned sintered alnico magnets for improved energy product and magnetic remanence, uniaxial stress was attempted to promote controlled grain growth, avoiding directional solidification that provides alignment in alnico 9. Successful development of solid-state powder processing may enable anisotropically aligned alnico magnets with enhanced energy density to be mass-produced
Policy Shocks and Market-Based Regulations: Evidence from the Renewable Fuel Standard
The Renewable Fuel Standard mandates large increases in U.S. biofuel consumption and is implemented using tradable compliance credits known as RINs. In early 2013, RIN prices soared, causing the regulator to propose reducing future mandates. We estimate empirically the effect of three âpolicy shocksâ that reduced the expected mandates in 2013. We find that the largest of these shocks decreased the value of the fuel industryâs 2013 compliance obligation by $7 billion. We then study the effects of the shocks on commodity markets and the market value of publicly traded biofuel firms. Results show that the burden of the mandate reductions fell primarily on advanced biofuel firms and commodity markets of the marginal compliance biofuel. We argue that the policy shocks reduced the incentive to invest in the technologies required to meet the future objectives of the RFS, and discuss alternative policy designs to address the problems that arose in 2013
Relative commutants of strongly self-absorbing C*-algebras
The relative commutant of a strongly self-absorbing
algebra is indistinguishable from its ultrapower . This
applies both to the case when is the hyperfinite II factor and to the
case when it is a strongly self-absorbing C*-algebra. In the latter case we
prove analogous results for and reduced powers
corresponding to other filters on . Examples of algebras with
approximately inner flip and approximately inner half-flip are provided,
showing the optimality of our results. We also prove that strongly
self-absorbing algebras are smoothly classifiable, unlike the algebras with
approximately inner half-flip.Comment: Some minor correction
The last frontier: Catch records of white sharks (carcharodon carcharias) in the northwest pacific ocean
White sharks are highly migratory apex predators, globally distributed in temperate, sub-tropical, and tropical waters. Knowledge of white shark biology and ecology has increased recently based on research at known aggregation sites in the Indian, Atlantic, and Northeast Pacific Oceans; however, few data are available for the Northwest Pacific Ocean. This study provides a meta-analysis of 240 observations of white sharks from the Northwest Pacific Ocean between 1951 and 2012. Records comprise reports of bycatch in commercial fisheries, media accounts, personal communications, and documentation of shark-human interactions from Russia (n = 8), Republic of Korea (22), Japan (129), China (32), Taiwan (45), Philippines (1) and Vietnam (3). Observations occurred in all months, excluding October-January in the north (Russia and Republic of Korea) and July-August in the south (China, Taiwan, Philippines, and Vietnam). Population trend analysis indicated that the relative abundance of white sharks in the region has remained relatively stable, but parameterization of a 75% increase in observer effort found evidence of a minor decline since 2002. Reliably measured sharks ranged from 126â 602 cm total length (TL) and 16â2530 kg total weight. The largest shark in this study (602 cm TL) represents the largest measured shark on record worldwide. For all countries combined the sex ratio was non-significantly biased towards females (1:1.1; n = 113). Of 60 females examined, 11 were confirmed pregnant ranging from the beginning stages of pregnancy (egg cases) to near term (140 cm TL embryos). On average, 6.062.2 embryos were found per litter (maximum of 10) and gestation period was estimated to be 20 months. These observations confirm that white sharks are present in the Northwest Pacific Ocean year-round. While acknowledging the difficulties of studying little known populations of a naturally low abundance species, these results highlight the need for dedicated research to inform regional conservation and management plannin
Long-Term Seizure Suppression and Optogenetic Analyses of Synaptic Connectivity in Epileptic Mice with Hippocampal Grafts of GABAergic Interneurons
Studies in rodent epilepsy models suggest that GABAergic interneuron progenitor grafts can reduce hyperexcitability and seizures in temporal lobe epilepsy (TLE). Although integration of the transplanted cells has been proposed as the underlying mechanism for these disease-modifying effects, prior studies have not explicitly examined cell types and synaptic mechanisms for long-term seizure suppression. To address this gap, we transplanted medial ganglionic eminence (MGE) cells from embryonic day 13.5 VGAT-Venus or VGAT-ChR2-EYFP transgenic embryos into the dentate gyrus (DG) of adult mice 2 weeks after induction of TLE with pilocarpine. Beginning 3â4 weeks after status epilepticus, we conducted continuous video-electroencephalographic recording until 90â100 d. TLE mice with bilateral MGE cell grafts in the DG had significantly fewer and milder electrographic seizures, compared with TLE controls. Immunohistochemical studies showed that the transplants contained multiple neuropeptide or calcium-binding protein-expressing interneuron types and these cells established dense terminal arborizations onto the somas, apical dendrites, and axon initial segments of dentate granule cells (GCs). A majority of the synaptic terminals formed by the transplanted cells were apposed to large postsynaptic clusters of gephyrin, indicative of mature inhibitory synaptic complexes. Functionality of these new inhibitory synapses was demonstrated by optogenetically activating VGAT-ChR2-EYFP-expressing transplanted neurons, which generated robust hyperpolarizations in GCs. These findings suggest that fetal GABAergic interneuron grafts may suppress pharmacoresistant seizures by enhancing synaptic inhibition in DG neural circuits
Very Red and Extremely Red Galaxies in the Fields of z ~ 1.5 Radio-Loud Quasars
We previously identified an excess of mostly red galaxies around 31 RLQs at
z=1-2. These fields have an ERO (extremely red object, R-K>6) density 2.7 times
higher than the field. Assuming the EROs are passively evolved galaxies at the
quasar redshifts, they have characteristic luminosities of only ~L^*. We also
present new observations of four z~1.54 RLQ fields: (1) Wide-field J & Ks data
confirm an Abell richness ~2 excess within 140" of Q0835+580 but an excess only
within 50" of Q1126+101. (2) In 3 fields we present deep narrow-band redshifted
H-alpha observations. We detect five candidate galaxies at the quasar
redshifts, a surface density 2.5x higher than the field. (3) SCUBA sub-mm
observations of 3 fields detect 2 quasars and 2 galaxies with SEDs best fit as
highly reddened galaxies at the quasar z. (4) H-band adaptive optics (AO)
imaging is used to estimate redshifts for 2 red, bulge-dominated galaxies using
the Kormendy relation. Both have structural redshifts foreground to the quasar,
but these are not confirmed by photometric redshifts, possibly because their
optical photometry is corrupted by scattered light from the AO guidestar. (5)
We use quantitative SED fits to constrain the photometric redshifts z_ph for
some galaxies. Most galaxies near Q0835+580 are consistent with being at its
redshift, including a candidate very old passively evolving galaxy. Many very &
extremely red objects have z_ph z_q, and dust reddening is required to fit most
of them, including many objects whose fits also require relatively old stellar
populations. Large reddenings of E(B-V)~0.6 are required to fit four J-K
selected EROs, though all but one of them have best-fit z_ph>z_q. These objects
may represent a population of dusty high-z galaxies underrepresented in
optically selected samples. (Abridged)Comment: Missing object 1126.424 added to Table 4; title changed to save
people the apparent trouble of reading the abstract. 38 pages, 16 figures, 2
in color; all-PostScript figure version available from
http://astro.princeton.edu/~pathall/tp3.ps.g
SARM1 depletion rescues NMNAT1-dependent photoreceptor cell death and retinal degeneration
Leber congenital amaurosis type nine is an autosomal recessive retinopathy caused by mutations of the NA
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