6,133 research outputs found
Realization of a feedback controlled flashing ratchet
A flashing ratchet transports diffusive particles using a time-dependent,
asymmetric potential. Particle speed is predicted to increase when a feedback
algorithm based on particle positions is used. We have experimentally realized
such a feedback ratchet using an optical line trap, and observed that use of
feedback increases velocity by up to an order of magnitude. We compare two
different feedback algorithms for small particle numbers, and find good
agreement with simulations. We also find that existing algorithms can be
improved to be more tolerant to feedback delay times
Understanding and applying fused [n] polynorbornane scaffolds in supramolecular chemistry
The research here provides a better understanding of how the fused [n]polynorbornane framework effects the binding of anions (by exploring a case of regioselective binding) as well as exploring new ways of incorporating the rigid framework into a natural setting (stapled peptide)
GPU enabled real-time optical frequency comb spectroscopy and photonic readout
We describe a GPU-enabled approach for real-time optical frequency comb
spectroscopy in which data is recorded, Fourier transformed, normalized, and
fit at data rates up to 2.2 GB/s. As an initial demonstration we have applied
this approach to rapidly interrogate the motion of an optomechanical
accelerometer through the use of an electro-optic frequency comb. However, we
note that this approach is readily amenable to both self-heterodyne and dual
comb spectrometers for molecular spectroscopy as well as photonic readout where
the approach's agility, speed, and simplicity are expected to enable future
improvements and applications
Setting sub-organellar sights: accurate targeting of multi-transmembrane-domain proteins to specific chloroplast membranes
Engineering novel chloroplast functions requires an
understanding of how to accurately target proteins
to specific chloroplast sub-compartments. This is
particularly difficult in the case of membrane proteins
where localization can be confounded by multiple
membrane types. In an elegant study, Singhal and
Fernandez (2017) have now provided greater insight
into this challenge by dissecting out the signals that
control differential targeting of two related proteins to
specific chloroplast membranes. Further development
of this information should inform attempts to direct
engineered proteins to specific sub-organellar membranes,
bringing about desired phenotypic changes
Fungal diversity regulates plant-soil feedbacks in temperate grassland
Feedbacks between plants and soil microbial communities play an important role in vegetation dynamics, but the underlying mechanisms remain unresolved. Here, we show that the diversity of putative pathogenic, mycorrhizal, and saprotrophic fungi is a primary regulator of plant-soil feedbacks across a broad range of temperate grassland plant species. We show that plant species with resource-acquisitive traits, such as high shoot nitrogen concentrations and thin roots, attract diverse communities of putative fungal pathogens and specialist saprotrophs, and a lower diversity of mycorrhizal fungi, resulting in strong plant growth suppression on soil occupied by the same species. Moreover, soil properties modulate feedbacks with fertile soils, promoting antagonistic relationships between soil fungi and plants. This study advances our capacity to predict plant-soil feedbacks and vegetation dynamics by revealing fundamental links between soil properties, plant resource acquisition strategies, and the diversity of fungal guilds in soil
Tomimatsu-Sato geometries, holography and quantum gravity
We analyze the Tomimatsu-Sato spacetime in the context of the
proposed Kerr/CFT correspondence. This 4-dimensional vacuum spacetime is
asymptotically flat and has a well-defined ADM mass and angular momentum, but
also involves several exotic features including a naked ring singularity, and
two disjoint Killing horizons separated by a region with closed timelike curves
and a rod-like conical singularity. We demonstrate that the near horizon
geometry belongs to a general class of Ricci-flat metrics with
symmetry that includes both the extremal Kerr and
extremal Kerr-bolt geometries. We calculate the central charge and temperature
for the CFT dual to this spacetime and confirm the Cardy formula reproduces the
Bekenstein-Hawking entropy. We find that all of the basic parameters of the
dual CFT are most naturally expressed in terms of charges defined intrinsically
on the horizon, which are distinct from the ADM charges in this geometry.Comment: 20+1 pages, 3 figures, changed title, expanded discussion, matches
version published in CQ
CLEAR I: Ages and Metallicities of Quiescent Galaxies at Derived from Deep Hubble Space Telescope Grism Data
We use deep \textit{Hubble Space Telescope} spectroscopy to constrain the
metallicities and (\editone{light-weighted}) ages of massive () galaxies selected to have quiescent stellar
populations at . The data include 12--orbit depth coverage with the
WFC3/G102 grism covering ~\AA\, at a spectral
resolution of taken as part of the CANDELS Lyman- Emission
at Reionization (CLEAR) survey. At , the spectra cover important
stellar population features in the rest-frame optical. We simulate a suite of
stellar population models at the grism resolution, fit these to the data for
each galaxy, and derive posterior likelihood distributions for metallicity and
age. We stack the posteriors for subgroups of galaxies in different redshift
ranges that include different combinations of stellar absorption features. Our
results give \editone{light-weighted ages of ~Gyr,
~Gyr, ~Gyr, and
~Gyr, \editone{for galaxies at , 1.2,
1.3, and 1.6. This} implies that most of the massive quiescent galaxies at
\% of their stellar mass by a redshift of }. The
posteriors give metallicities of \editone{~, ~, ~, and ~}. This is evidence
that massive galaxies had enriched rapidly to approximately Solar metallicities
as early as .Comment: 32 pages, 23 figures, Resubmited to ApJ after revisions in response
to referee repor
The antisense oligonucleotide nusinersen for treatment of spinal muscular atrophy
Spinal muscular atrophy (SMA) is a rare, autosomal recessive neuromuscular degenerative disease characterized by loss of spinal cord motor neurons leading to progressive muscle wasting. The most common pathology results from a homozygous disruption in the survival motor neuron 1 (SMN1) gene on chromosome 5q13 via deletion, conversion, or mutation. SMN2 is a near duplicate of SMN1 that can produce full-length SMN mRNA transcripts, but its overall production capability of these mRNA transcripts is lower than that seen in SMN1. This leads to lower levels of functional SMN protein within motor neurons. The FDA approved nusinersen in December 2016 to treat SMA associated with SMN1 gene mutation. It is administered directly to the central nervous system by intrathecal injection. An antisense oligonucleotide (ASO) drug, nusinersen, provides an upcoming and promising treatment option for SMA and represents a novel pharmacological approach with a mechanism of action relevant for other neurodegenerative disorders. Nusinersen begins with four initial loading doses that are followed by three maintenance doses per year. Three major studies (CHERISH, ENDEAR, and NURTURE) have shown to improve motor function in early and late-onset individuals and reduce the chances of ventilator requirements in pre-symptomatic infants. Studies investigating the timing of drug delivery in mouse models of SMA report the best outcomes when drugs are delivered early before any significant motor function is lost. Nusinersen is a novel therapeutic approach with consistent results in all three studies and is proof of the novel concept for treating SMA and other neurodegenerative disorders in the future
Implementing a Registry Federation for Materials Science Data Discovery
As a result of a number of national initiatives, we are seeing rapid growth in the data important to materials science that are available over the web. Consequently, it is becoming increasingly difficult for researchers to learn what data are available and how to access them. To address this problem, the Research Data Alliance (RDA) Working Group for International Materials Science Registries (IMRR) was established to bring together materials science and information technology experts to develop an international federation of registries that can be used for global discovery of data resources for materials science. A resource registry collects high-level metadata descriptions of resources such as data repositories, archives, websites, and services that are useful for data-driven research. By making the collection searchable, it aids scientists in industry, universities, and government laboratories to discover data relevant to their research and work interests.
We present the results of our successful piloting of a registry federation for materials science data discovery. In particular, we out a blueprint for creating such a federation that is capable of amassing a global view of all available materials science data, and we enumerate the requirements for the standards that make the registries interoperable within the federation. These standards include a protocol for exchanging resource descriptions and a standard metadata schema for encoding those descriptions. We summarize how we leveraged an existing standard (OAI-PMH) for metadata exchange. Finally, we review the registry software developed to realize the federation and describe the user experience
- …