2,784 research outputs found
Magnetic polarons and magnetoresistance in EuB6
EuB6 is a low carrier density ferromagnet which exhibits large
magnetoresistance, positive or negative depending on temperature. The formation
of magnetic polarons just above the magnetic critical temperature has been
suggested by spin-flip Raman scattering experiments. We find that the fact that
EuB6 is a semimetal has to be taken into account to explain its electronic
properties, including magnetic polarons and magnetoresistance.Comment: 6 pages, 1 figur
Wiring up pre-characterized single-photon emitters by laser lithography
Future quantum optical chips will likely be hybrid in nature and include many single-photon emitters, waveguides, filters, as well as single-photon detectors. Here, we introduce a scalable optical localization-selection-lithography procedure for wiring up a large number of single-photon emitters via polymeric photonic wire bonds in three dimensions. First, we localize and characterize nitrogen vacancies in nanodiamonds inside a solid photoresist exhibiting low background fluorescence. Next, without intermediate steps and using the same optical instrument, we perform aligned three-dimensional laser lithography. As a proof of concept, we design, fabricate, and characterize three-dimensional functional waveguide elements on an optical chip. Each element consists of one single-photon emitter centered in a crossed-arc waveguide configuration, allowing for integrated optical excitation and efficient background suppression at the same time
Processing Succinct Matrices and Vectors
We study the complexity of algorithmic problems for matrices that are
represented by multi-terminal decision diagrams (MTDD). These are a variant of
ordered decision diagrams, where the terminal nodes are labeled with arbitrary
elements of a semiring (instead of 0 and 1). A simple example shows that the
product of two MTDD-represented matrices cannot be represented by an MTDD of
polynomial size. To overcome this deficiency, we extended MTDDs to MTDD_+ by
allowing componentwise symbolic addition of variables (of the same dimension)
in rules. It is shown that accessing an entry, equality checking, matrix
multiplication, and other basic matrix operations can be solved in polynomial
time for MTDD_+-represented matrices. On the other hand, testing whether the
determinant of a MTDD-represented matrix vanishes PSPACE$-complete, and the
same problem is NP-complete for MTDD_+-represented diagonal matrices. Computing
a specific entry in a product of MTDD-represented matrices is #P-complete.Comment: An extended abstract of this paper will appear in the Proceedings of
CSR 201
Sugarcoated isolation: Evidence that social avoidance is linked to higher basal glucose levels and higher consumption of glucose
Objective: The human brain adjusts its level of effort in coping with various life stressors as a partial function of perceived access to social resources. We examined whether people who avoid social ties maintain a higher fasting basal level of glucose in their bloodstream, reflecting a strategy to draw more on personal resources when threatened.Methods: For Study 1, we obtained fasting blood glucose and adult attachment orientations data from 60 undergraduate women at the University of Virginia. For Study 2, we collected measures of fasting blood glucose, self-reported trait anxiety, DHEA-cortisol, hypertension, and adult attachment orientations from 285 older adults of mixed gender, using a measure of attachment style different from study 1.Results: In study 1, fasting blood glucose levels corresponded with higher attachment avoidance scores after statistically adjusting for interpersonal anxiety. For study 2, fasting blood glucose continued to correspond with higher adult attachment avoidance even after statistically adjusting for interpersonal anxiety, trait anxiety, DHEA-cortisol and hypertension. Conclusions: Results suggest socially avoidant individuals upwardly adjust their basal glucose levels with the expectation of increased personal effort because of limited access to social resources
The beginnings of geography teaching and research in the University of Glasgow: the impact of J.W. Gregory
J.W. Gregory arrived in Glasgow from Melbourne in 1904 to take up the post of foundation Professor of Geology in the University of Glasgow. Soon after his arrival in Glasgow he began to push for the setting up of teaching in Geography in Glasgow, which came to pass in 1909 with the appointment of a Lecturer in Geography. This lecturer was based in the Department of Geology in the University's East Quad. Gregory's active promotion of Geography in the University was matched by his extensive writing in the area, in textbooks, journal articles and popular books. His prodigious output across a wide range of subject areas is variably accepted today, with much of his geomorphological work being judged as misguided to varying degrees. His 'social science' publications - in the areas of race, migration, colonisation and economic development of Africa and Australia - espouse a viewpoint that is unacceptable in the twenty-first century. Nonetheless, that viewpoint sits squarely within the social and economic traditions of Gregory's era, and he was clearly a key 'Establishment' figure in natural and social sciences research in the first half of the twentieth century. The establishment of Geography in the University of Glasgow remains enduring testimony of J.W. Gregory's energy, dedication and foresight
Fluctuation induced hopping and spin polaron transport
We study the motion of free magnetic polarons in a paramagnetic background of
fluctuating local moments. The polaron can tunnel only to nearby regions of
local moments when these fluctuate into alignment. We propose this fluctuation
induced hopping as a new transport mechanism for the spin polaron. We calculate
the diffusion constant for fluctuation induced hopping from the rate at which
local moments fluctuate into alignment. The electrical resistivity is then
obtained via the Einstein relation. We suggest that the proposed transport
mechanism is relevant in the high temperature phase of the Mn pyrochlore
colossal magneto resistance compounds and Europium hexaboride.Comment: 8 pages, 3 figure
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