357 research outputs found
Why talking won’t help presidents win bipartisan support
Do presidents unite or divide Congress? In new research which analyses more than 6,000 roll call votes over nearly 40 years, Travis J. Baker finds that members of the opposition party are about 6 percent less likely to support a president’s priorities than members of the president’s party. This occurs even when legislators have the same voting record, and the differences get wider as presidents speak for longer on the issue. He argues that this effect is mainly driven by divided government, since at those times Congress is more likely to vote for bills which are opposed to the president’s agenda
The Heisenberg limit for laser coherence
To quantify quantum optical coherence requires both the particle- and
wave-natures of light. For an ideal laser beam [1,2,3], it can be thought of
roughly as the number of photons emitted consecutively into the beam with the
same phase. This number, , can be much larger than , the
number of photons in the laser itself. The limit on for an ideal
laser was thought to be of order [4,5]. Here, assuming nothing about
the laser operation, only that it produces a beam with certain properties close
to those of an ideal laser beam, and that it does not have external sources of
coherence, we derive an upper bound: . Moreover, using
the matrix product states (MPSs) method [6,7,8,9], we find a model that
achieves this scaling, and show that it could in principle be realised using
circuit quantum electrodynamics (QED) [10]. Thus is
only a standard quantum limit (SQL); the ultimate quantum limit, or Heisenberg
limit, is quadratically better.Comment: 6 pages, 4 figures, and 31 pages of supplemental information. v2:
This paper is now published [Nature Physics DOI:10.1038/s41567-020-01049-3
(26 October 2020)]. For copyright reasons, this arxiv paper is based on a
version of the paper prior to the accepted (21 August 2020) versio
On-farm food loss in northern and central California: Results of field survey measurementsAuthor links open overlay panel
Prevailing estimates of food loss at the farm level are sparse and often reliant upon grower surveys. A more comprehensive review of food loss at the farm level using field surveys is required to gain an adequate understanding of the depth of this issue. This paper details the results of 123 in-field surveys and 18 in-depth interviews of 20 different, hand-harvested field crops performed largely on midsize to large conventional farms in northern and central California. We also provide estimates of the percentage of fields that go unharvested, commonly known as walk-by fields. The results show that food loss is highly variable and largely dependent upon the crop, variety, market price, labor costs, grower practices, buyer specifications, and environmental conditions. On average, we found 11,299 kg/ha of food loss at the farm level, which equates to 31.3% of the marketed yield. When walk-by losses are included, this figure rises to 33.7%. Our paper also demonstrates that grower estimates are typically very unreliable for estimating on-farm food losses. Actual, measured edible food loss exceeded growers’ estimates by a median value of 157%. Strategies to utilize this lost produce could play a significant role in reducing the impact of agriculture on the environment and providing food for the rapidly growing population
Necessary condition for steerability of arbitrary two-qubit states with loss
Einstein-Podolsky-Rosen steering refers to the quantum phenomenon whereby the
state of a system held by one party can be "steered" into different states at
the will of another, distant, party by performing different local measurements.
Although steering has been demonstrated in a number of experiments involving
qubits, the question of which two-qubit states are steerable remains an open
theoretical problem. Here, we derive a necessary condition for any two-qubit
state to be steerable when the steering party suffers from a given probability
of qubit loss. Our main result finds application in one-way steering
demonstrations that rely upon loss. Specifically, we apply it to a recent
experiment on one-way steering with projective measurements and POVMs, reported
by Wollmann et. al. [Phys. Rev. Lett., 116, 160403 (2016)].Comment: 7 pages, 1 figur
The role of ARX in human pancreatic endocrine specification
The in vitro differentiation of human embryonic stem cells (hESCs) offers a model system to explore human development. Humans with mutations in the transcription factor Aristaless Related Homeobox (ARX) often suffer from the syndrome X-linked lissencephaly with ambiguous genitalia (XLAG), affecting many cell types including those of the pancreas. Indeed, XLAG pancreatic islets lack glucagon and pancreatic polypeptide-positive cells but retain somatostatin, insulin, and ghrelin-positive cells. To further examine the role of ARX in human pancreatic endocrine development, we utilized genomic editing in hESCs to generate deletions in ARX. ARX knockout hESCs retained pancreatic differentiation capacity and ARX knockout endocrine cells were biased toward somatostatin-positive cells (94% of endocrine cells) with reduced pancreatic polypeptide (rarely detected), glucagon (90% reduced) and insulin-positive (65% reduced) lineages. ARX knockout somatostatin-positive cells shared expression patterns with human fetal and adult δ-cells. Differentiated ARX knockout cells upregulated PAX4, NKX2.2, ISL1, HHEX, PCSK1, PCSK2 expression while downregulating PAX6 and IRX2. Re-expression of ARX in ARX knockout pancreatic progenitors reduced HHEX and increased PAX6 and insulin expression following differentiation. Taken together these data suggest that ARX plays a key role in pancreatic endocrine fate specification of pancreatic polypeptide, somatostatin, glucagon and insulin positive cells from hESCs
Scalable multiparty steering based on a single pair of entangled qubits
The distribution and verification of quantum nonlocality across a network of
users is essential for future quantum information science and technology
applications. However, beyond simple point-to-point protocols, existing methods
struggle with increasingly complex state preparation for a growing number of
parties. Here, we show that, surprisingly, multiparty loophole-free quantum
steering, where one party simultaneously steers arbitrarily many spatially
separate parties, is achievable by constructing a quantum network from a set of
qubits of which only one pair is entangled. Using these insights, we
experimentally demonstrate this type of steering between three parties with the
detection loophole closed. With its modest and fixed entanglement requirements,
this work introduces a scalable approach to rigorously verify quantum
nonlocality across multiple parties, thus providing a practical tool towards
developing the future quantum internet
Conclusive experimental demonstration of one-way Einstein-Podolsky-Rosen steering
Einstein-Podolsky-Rosen steering is a quantum phenomenon wherein one party
influences, or steers, the state of a distant party's particle beyond what
could be achieved with a separable state, by making measurements on one half of
an entangled state. This type of quantum nonlocality stands out through its
asymmetric setting, and even allows for cases where one party can steer the
other, but where the reverse is not true. A series of experiments have
demonstrated one-way steering in the past, but all were based on significant
limiting assumptions. These consisted either of restrictions on the type of
allowed measurements, or of assumptions about the quantum state at hand, by
mapping to a specific family of states and analysing the ideal target state
rather than the real experimental state. Here, we present the first
experimental demonstration of one-way steering free of such assumptions. We
achieve this using a new sufficient condition for non-steerability, and,
although not required by our analysis, using a novel source of extremely
high-quality photonic Werner states.Comment: Supplemental Material included in the documen
(Re)Storying Obama: An Examination of Recently Published Informational Texts
American publishers have published numerous children’s books about Barack Obama over the past several years; most take the form of informational biographies. This article reports on a research project aimed at how these books incorporate sociohistorical narratives, particularly those related to the civil rights movement. Though the features of the books might cause the reader to presume political neutrality, the books link readers to distinct Discourses (Gee, 1996), suggesting particular ideologies. In this article, we identified the following differences: (1) specific happenings from Obama’s life were included in some texts while omitted in others; (2) when the events were included, how they were framed differed; and (3) the narrative constructions of the events varied. We use the differences amongst these texts to argue for the importance of critical literacy in elementary classrooms
An empirical evaluation of camera trap study design: How many, how long and when?
Abstract
Camera traps deployed in grids or stratified random designs are a well‐established survey tool for wildlife but there has been little evaluation of study design parameters.
We used an empirical subsampling approach involving 2,225 camera deployments run at 41 study areas around the world to evaluate three aspects of camera trap study design (number of sites, duration and season of sampling) and their influence on the estimation of three ecological metrics (species richness, occupancy and detection rate) for mammals.
We found that 25–35 camera sites were needed for precise estimates of species richness, depending on scale of the study. The precision of species‐level estimates of occupancy (ψ) was highly sensitive to occupancy level, with 0.75) species, but more than 150 camera sites likely needed for rare (ψ < 0.25) species. Species detection rates were more difficult to estimate precisely at the grid level due to spatial heterogeneity, presumably driven by unaccounted habitat variability factors within the study area. Running a camera at a site for 2 weeks was most efficient for detecting new species, but 3–4 weeks were needed for precise estimates of local detection rate, with no gains in precision observed after 1 month. Metrics for all mammal communities were sensitive to seasonality, with 37%–50% of the species at the sites we examined fluctuating significantly in their occupancy or detection rates over the year. This effect was more pronounced in temperate sites, where seasonally sensitive species varied in relative abundance by an average factor of 4–5, and some species were completely absent in one season due to hibernation or migration.
We recommend the following guidelines to efficiently obtain precise estimates of species richness, occupancy and detection rates with camera trap arrays: run each camera for 3–5 weeks across 40–60 sites per array. We recommend comparisons of detection rates be model based and include local covariates to help account for small‐scale variation. Furthermore, comparisons across study areas or times must account for seasonality, which could have strong impacts on mammal communities in both tropical and temperate sites
- …