3,704 research outputs found
Preliminary results of passive microwave snow experiment during February and March 1978
The purpose of the experiment was to determine if remote microwave sensing of snowpack data could be used to predict runoff, thereby allowing more efficient management of the water supply. A four-frequency microwave radiometer system was attached to a truck-mounted aerial lift and was used to gather data on snowpacks at three different sites in the Colorado Rocky Mountains. Ground truth data measurements (density, temperature, grain size, hardness, and free-liquid water content) were taken at each site corresponding to each microwave scan
Device calibration impacts security of quantum key distribution
Characterizing the physical channel and calibrating the cryptosystem hardware
are prerequisites for establishing a quantum channel for quantum key
distribution (QKD). Moreover, an inappropriately implemented calibration
routine can open a fatal security loophole. We propose and experimentally
demonstrate a method to induce a large temporal detector efficiency mismatch in
a commercial QKD system by deceiving a channel length calibration routine. We
then devise an optimal and realistic strategy using faked states to break the
security of the cryptosystem. A fix for this loophole is also suggested.Comment: 4 pages + 1 page of supplementary information. Considerable
modification of Eve's attack strategy and QBER minimization technique. All
figures have also been improve
Feasibility of free space quantum key distribution with coherent polarization states
We demonstrate for the first time the feasibility of free space quantum key
distribution with continuous variables under real atmospheric conditions. More
specifically, we transmit coherent polarization states over a 100m free space
channel on the roof of our institute's building. In our scheme, signal and
local oscillator are combined in a single spatial mode which auto-compensates
atmospheric fluctuations and results in an excellent interference. Furthermore,
the local oscillator acts as spatial and spectral filter thus allowing
unrestrained daylight operation.Comment: 12 pages, 8 figures, extensions in sections 2, 3.1, 3.2 and 4. This
is an author-created, un-copyedited version of an article accepted for
publication in New Journal of Physics (Special Issue on Quantum Cryptography:
Theory and Practice). IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
Reinventing College Physics for Biologists: Explicating an epistemological curriculum
The University of Maryland Physics Education Research Group (UMd-PERG)
carried out a five-year research project to rethink, observe, and reform
introductory algebra-based (college) physics. This class is one of the Maryland
Physics Department's large service courses, serving primarily life-science
majors. After consultation with biologists, we re-focused the class on helping
the students learn to think scientifically -- to build coherence, think in
terms of mechanism, and to follow the implications of assumptions. We designed
the course to tap into students' productive conceptual and epistemological
resources, based on a theoretical framework from research on learning. The
reformed class retains its traditional structure in terms of time and
instructional personnel, but we modified existing best-practices curricular
materials, including Peer Instruction, Interactive Lecture Demonstrations, and
Tutorials. We provided class-controlled spaces for student collaboration, which
allowed us to observe and record students learning directly. We also scanned
all written homework and examinations, and we administered pre-post conceptual
and epistemological surveys. The reformed class enhanced the strong gains on
pre-post conceptual tests produced by the best-practices materials while
obtaining unprecedented pre-post gains on epistemological surveys instead of
the traditional losses.Comment: 35 pages including a 15 page appendix of supplementary material
Cosmogenic 10BE and 26AL studies of the rising star site, Cradle of Humankind, South Africa: mystery of the true denudation rates
Based on 10Be denudation rates previously found (3.6 m/Ma, [2]; 3.44 m/Ma, [1]), the landscape across the CoH is considered old and eroding slowly. High erosion rates similar to our results (5.13 - 15.02 m/Ma) for chert bedrock are ascribed to fast river incision or a recent partial collapse event [1,2]. In contrast, we think our high outcrop erosion rates reflect true denudation and low apparent values from soil samples indicate long retention of quartz on surface, while dolomite is largely removed in solution. The quartz then experiences periods of burial and reworking in caves and river terraces, resulting in low 26Al/10Be ratios
The Object Coordination Class Applied to Wavepulses: Analysing Student Reasoning in Wave Physics
Detailed investigations of student reasoning show that students approach the
topic of wave physics using both event-like and object-like descriptions of
wavepulses, but primarily focus on object properties in their reasoning.
Student responses to interview and written questions are analysed using diSessa
and Sherin's coordination class model which suggests that student use of
specific reasoning resources is guided by possibly unconscious cues. Here, the
term reasoning resources is used in a general fashion to describe any of the
smaller grain size models of reasoning (p-prims, facets of knowledge, intuitive
rules, etc) rather than theoretically ambiguous (mis)conceptions. Student
applications of reasoning resources, including one previously undocumented, are
described. Though the coordination class model is extremely helpful in
organising the research data, problematic aspects of the model are also
discussed.Comment: 20 pages, 8 figures, 27 reference
Machine learning-assisted directed protein evolution with combinatorial libraries
To reduce experimental effort associated with directed protein evolution and
to explore the sequence space encoded by mutating multiple positions
simultaneously, we incorporate machine learning in the directed evolution
workflow. Combinatorial sequence space can be quite expensive to sample
experimentally, but machine learning models trained on tested variants provide
a fast method for testing sequence space computationally. We validate this
approach on a large published empirical fitness landscape for human GB1 binding
protein, demonstrating that machine learning-guided directed evolution finds
variants with higher fitness than those found by other directed evolution
approaches. We then provide an example application in evolving an enzyme to
produce each of the two possible product enantiomers (stereodivergence) of a
new-to-nature carbene Si-H insertion reaction. The approach predicted libraries
enriched in functional enzymes and fixed seven mutations in two rounds of
evolution to identify variants for selective catalysis with 93% and 79% ee. By
greatly increasing throughput with in silico modeling, machine learning
enhances the quality and diversity of sequence solutions for a protein
engineering problem.Comment: Corrected best S-selective variant sequence in Figure 4. Corrected
less R-selective variant sequences from Round II Input library in Table 2 and
Supp Table 4. Corrections may also be found on PNAS version
https://www.pnas.org/content/early/2019/12/26/192177011
Integrable atomtronic interferometry
High sensitivity quantum interferometry requires more than just access to
entangled states. It is achieved through deep understanding of quantum
correlations in a system. Integrable models offer the framework to develop this
understanding. We communicate the design of interferometric protocols for an
integrable model that describes the interaction of bosons in a four-site
configuration. Analytic formulae for the quantum dynamics of certain
observables are computed. These expose the system's functionality as both an
interferometric identifier, and producer, of NOON states. Being equivalent to a
controlled-phase gate acting on two hybrid qudits, this system also highlights
an equivalence between Heisenberg-limited interferometry and quantum
information. These results are expected to open new avenues for
integrability-enhanced atomtronic technologies.Comment: 6 pages, 4 figures, 1 tabl
Hacking commercial quantum cryptography systems by tailored bright illumination
The peculiar properties of quantum mechanics allow two remote parties to
communicate a private, secret key, which is protected from eavesdropping by the
laws of physics. So-called quantum key distribution (QKD) implementations
always rely on detectors to measure the relevant quantum property of single
photons. Here we demonstrate experimentally that the detectors in two
commercially available QKD systems can be fully remote-controlled using
specially tailored bright illumination. This makes it possible to tracelessly
acquire the full secret key; we propose an eavesdropping apparatus built of
off-the-shelf components. The loophole is likely to be present in most QKD
systems using avalanche photodiodes to detect single photons. We believe that
our findings are crucial for strengthening the security of practical QKD, by
identifying and patching technological deficiencies.Comment: Revised version, rewritten for clarity. 5 pages, 5 figures. To
download the Supplementary information (which is in open access), go to the
journal web site at http://dx.doi.org/10.1038/nphoton.2010.21
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