9,674 research outputs found
Impurity Effects and Spin Polarizations in a Narrow Quantum Hall System
The temperature dependence of electron spin polarization for a narrow quantum
Hall system shows behavior analogous to that of a two-dimensional system at
major filling factors. At the lowest half-filled quantum Hall state for which
no two-dimensional analog exists, we find a stable spin partially-polarized
system. Periodic Gaussian repulsive impurities (antidots) in such a system
leads to novel spin transitions at and and the
pair-correlation functions provide clues about nature of different ground
states in the system. These results can be explored in optical spectroscopy and
optically pumped NMR Knight shift measurements.Comment: 4 pages, REVTEX, and 4 .ps file
Identification of drug resistance mutations in HIV from constraints on natural evolution
Human immunodeficiency virus (HIV) evolves with extraordinary rapidity.
However, its evolution is constrained by interactions between mutations in its
fitness landscape. Here we show that an Ising model describing these
interactions, inferred from sequence data obtained prior to the use of
antiretroviral drugs, can be used to identify clinically significant sites of
resistance mutations. Successful predictions of the resistance sites indicate
progress in the development of successful models of real viral evolution at the
single residue level, and suggest that our approach may be applied to help
design new therapies that are less prone to failure even where resistance data
is not yet available.Comment: 5 pages, 3 figure
Equality of Voice: Towards Fair Representation in Crowdsourced Top-K Recommendations
To help their users to discover important items at a particular time, major
websites like Twitter, Yelp, TripAdvisor or NYTimes provide Top-K
recommendations (e.g., 10 Trending Topics, Top 5 Hotels in Paris or 10 Most
Viewed News Stories), which rely on crowdsourced popularity signals to select
the items. However, different sections of a crowd may have different
preferences, and there is a large silent majority who do not explicitly express
their opinion. Also, the crowd often consists of actors like bots, spammers, or
people running orchestrated campaigns. Recommendation algorithms today largely
do not consider such nuances, hence are vulnerable to strategic manipulation by
small but hyper-active user groups.
To fairly aggregate the preferences of all users while recommending top-K
items, we borrow ideas from prior research on social choice theory, and
identify a voting mechanism called Single Transferable Vote (STV) as having
many of the fairness properties we desire in top-K item (s)elections. We
develop an innovative mechanism to attribute preferences of silent majority
which also make STV completely operational. We show the generalizability of our
approach by implementing it on two different real-world datasets. Through
extensive experimentation and comparison with state-of-the-art techniques, we
show that our proposed approach provides maximum user satisfaction, and cuts
down drastically on items disliked by most but hyper-actively promoted by a few
users.Comment: In the proceedings of the Conference on Fairness, Accountability, and
Transparency (FAT* '19). Please cite the conference versio
Deconvolving mutational patterns of poliovirus outbreaks reveals its intrinsic fitness landscape.
Vaccination has essentially eradicated poliovirus. Yet, its mutation rate is higher than that of viruses like HIV, for which no effective vaccine exists. To investigate this, we infer a fitness model for the poliovirus viral protein 1 (vp1), which successfully predicts in vitro fitness measurements. This is achieved by first developing a probabilistic model for the prevalence of vp1 sequences that enables us to isolate and remove data that are subject to strong vaccine-derived biases. The intrinsic fitness constraints derived for vp1, a capsid protein subject to antibody responses, are compared with those of analogous HIV proteins. We find that vp1 evolution is subject to tighter constraints, limiting its ability to evade vaccine-induced immune responses. Our analysis also indicates that circulating poliovirus strains in unimmunized populations serve as a reservoir that can seed outbreaks in spatio-temporally localized sub-optimally immunized populations
A new deterministic model of strange stars
The observed evidence for the existence of strange stars and the concomitant
observed masses and radii are used to derive an interpolation formula for the
mass as a function of the radial coordinate. The resulting general mass
function becomes an effective model for a strange star. The analysis is based
on the MIT bag model and yields the energy density, as well as the radial and
transverse pressures. Using the interpolation function for the mass, it is
shown that a mass-radius relation due to Buchdahl is satisfied in our model. We
find the surface redshift () corresponding to the compactness of the stars.
Finally, from our results, we predict some characteristics of a strange star of
radius 9.9 km.Comment: one new figures and minor revisions have been done. To appear in
Eur.Phys.J.
Somatic chromosomes of two marine teleosts
Somatic chromosomes of two species of sciaenids Otolithes cuvieri (Trewavas)
and Nibea diacanthus (Lacepede) are reported here. Chromosome preparations were
made using colchicine-citrate-acelo-methanol-air drying technique using tissue from
kidney, stomach, gills and intestine. Both the species gave a diploid oount of 48 acrocentric
chromosomes
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