835 research outputs found
Electron correlation and magnetism at the LaAlO/SrTiO interface: A DFT+DMFT investigation
We shed light on the interplay between structure and many-body effects
relevant for itinerant ferromagnetism in LaAlO/SrTiO heterostructures.
The realistic correlated electronic structure is studied by means of the
(spin-polarized) charge self-consistent combination of density functional
theory (DFT) with dynamical mean-field theory (DMFT) beyond the realm of static
correlation effects. Though many-body behavior is also active in the
defect-free interface, a ferromagnetic instability occurs only with oxygen
vacancies. A minimal Ti two-orbital - description for the
correlated subspace is derived. Magnetic order affected by quantum fluctuations
builds up from effective double exchange between nearly-localized and
mobile electrons.Comment: refinements, final versio
What Can We Learn from Exam Grade Distributions?
A course with good learning outcomes is one in which most of the enrolled students achieve the mastery specified in the predefined learning objectives. Since the enrolment is invariably a mix of students with heterogeneous capabilities, the class average grade is a poor indicator of how the class is divided into at least two groups, of high- and low-performers. Clearly, achieving the desired outcomes implies increasing the proportion of high-performing students and their mean grade by providing appropriately designed teaching protocols. In this paper, the actual class grade distribution is approximated by a bimodal probability distribution function, whose parameters enable the proportions and average performance of these two groups to be quantified. This paper describes the methodology to achieve this and demonstrates its usage to diagnose example exam grade distributions, as well as to provide quantification of the impact of pedagogic changes on the degree of achieving teaching objectives
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Checking Polynomial Identities over any Field: Towards a Derandomization?
We present a Monte Carlo algorithm for testing multivariate polynomial identities over any field using fewer random bits than other methods. To test if a polynomial is zero, our method uses random bits, where is the degree of in , to obtain any inverse polynomial error in polynomial time. The algorithm applies to polynomials given as a black box or in some implicit representation such as a straight-line program. Our method works by evaluating P at truncated formal power series representing square roots of irreducible polynomials over the field. This approach is similar to that of Chen and Kao (STOC '97), but with the advantage that the techniques are purely algebraic and apply to any field. We also prove a lower bound showing that the number of random bits used by our algorithm is essentially optimal in the black-box model.Engineering and Applied Science
Formation of orbital-selective electron states in LaTiO/SrTiO superlattices
The interface electronic structure of correlated LaTiO/SrTiO
superlattices is investigated by means of the charge self-consistent
combination of the local density approximation (LDA) to density functional
theory (DFT) with dynamical mean-field theory (DMFT). Utilizing a
pseudopotential technique together with a continuous-time quantum Monte-Carlo
approach, the resulting complex multiorbital electronic states are addressed in
a coherent fashion beyond static mean-field. General structural relaxations are
taken into account on the LDA level and cooperate with the driving forces from
strong electronic correlations. This alliance leads to an Ti()
dominated low-energy quasiparticle peak and a lower Hubbard band in line with
photoemission studies. Furthermore correlation effects close to the
band-insulating bulk SrTiO limit as well as the Mott-insulating bulk
LaTiO limit are studied via realistic single-layer embeddings.Comment: minor refinements, added referenc
Electronic correlations in vanadium chalcogenides: BaVSe3 versus BaVS3
Albeit structurally and electronically very similar, at low temperature the
quasi-one-dimensional vanadium sulfide BaVS3 shows a metal-to-insulator
transition via the appearance of a charge-density-wave state, while BaVSe3
apparently remains metallic down to zero temperature. This different behavior
upon cooling is studied by means of density functional theory and its
combination with the dynamical mean-field theory and the rotationally-invariant
slave-boson method. We reveal several subtle differences between these
chalcogenides that provide indications for the deviant behavior of BaVSe3 at
low temperature. In this regard, a smaller Hubbard U in line with an increased
relevance of the Hund's exchange J plays a vital role.Comment: 16 pages, 11 figures, published versio
A Cure for HIV Infection: "Not in My Lifetime" or "Just Around the Corner"?
With the advent and stunning success of combination antiretroviral therapy (ART) to prolong and improve quality of life for persons with HIV infection, HIV research has been afforded the opportunity to pivot towards studies aimed at finding "a cure." The mere idea that cure of HIV might be possible has energized researchers and the community towards achieving this goal. Funding agencies, both governmental and private, have targeted HIV cure as a high priority; many in the field have responded to these initiatives and the cure research agenda is robust. In this "salon" two editors of Pathogens and Immunity, Michael Lederman and Daniel Douek ask whether curing HIV is a realistic, scalable objective. We start with an overview perspective and have asked a number of prominent HIV researchers to add to the discussion
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Defining and distinguishing infant behavioral states using acoustic cry analysis: is colic painful?
BackgroundTo characterize acoustic features of an infant's cry and use machine learning to provide an objective measurement of behavioral state in a cry-translator. To apply the cry-translation algorithm to colic hypothesizing that these cries sound painful.MethodsAssessment of 1000 cries in a mobile app (ChatterBabyTM). Training a cry-translation algorithm by evaluating >6000 acoustic features to predict whether infant cry was due to a pain (vaccinations, ear-piercings), fussy, or hunger states. Using the algorithm to predict the behavioral state of infants with reported colic.ResultsThe cry-translation algorithm was 90.7% accurate for identifying pain cries, and achieved 71.5% accuracy in discriminating cries from fussiness, hunger, or pain. The ChatterBaby cry-translation algorithm overwhelmingly predicted that colic cries were most likely from pain, compared to fussy and hungry states. Colic cries had average pain ratings of 73%, significantly greater than the pain measurements found in fussiness and hunger (p < 0.001, 2-sample t test). Colic cries outranked pain cries by measures of acoustic intensity, including energy, length of voiced periods, and fundamental frequency/pitch, while fussy and hungry cries showed reduced intensity measures compared to pain and colic.ConclusionsAcoustic features of cries are consistent across a diverse infant population and can be utilized as objective markers of pain, hunger, and fussiness. The ChatterBaby algorithm detected significant acoustic similarities between colic and painful cries, suggesting that they may share a neuronal pathway
Searching for Inflow Towards Massive Starless Clump Candidates Identified in the Bolocam Galactic Plane Survey
Recent Galactic plane surveys of dust continuum emission at long wavelengths
have identified a population of dense, massive clumps with no evidence for
on-going star formation. These massive starless clump candidates are excellent
sites to search for the initial phases of massive star formation before the
feedback from massive star formation effects the clump. In this study, we
search for the spectroscopic signature of inflowing gas toward starless clumps,
some of which are massive enough to form a massive star. We observed 101
starless clump candidates identified in the Bolocam Galactic Plane Survey
(BGPS) in HCO+ J = 1-0 using the 12m Arizona Radio Observatory telescope. We
find a small blue excess of E = (Nblue - Nred)/Ntotal = 0.03 for the complete
survey. We identified 6 clumps that are good candidates for inflow motion and
used a radiative transfer model to calculate mass inflow rates that range from
500 - 2000 M /Myr. If the observed line profiles are indeed due to large-scale
inflow motions, then these clumps will typically double their mass on a free
fall time. Our survey finds that massive BGPS starless clump candidates with
inflow signatures in HCO+ J = 1-0 are rare throughout our Galaxy.Comment: 14 pages, 9 figure
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