440 research outputs found
Remarks on the Myers-Perry and Einstein Gauss-Bonnet Rotating Solutions
The Kerr-type solutions of the five-dimensional Einstein and
Einstein-Gauss-Bonnet equations look pretty similar when written in Kerr-Schild
form. However the Myers-Perry spacetime is circular whereas the rotating
solution of the Einstein-Gauss-Bonnet theory is not. We explore some
consequences of this difference in particular regarding the (non) existence of
Boyer-Lindquist-type coordinates and the extension of the manifold
Facebook\u27s Free Basics and Implications for Development: IT Identity and Social Capital
Facebook\u27s Free Basics has been controversial among researchers in the fields of information and communication technologies for development (ICTD) and community informatics (CI). What is the nature of Free Basics\u27 potential contribution to individual and community development? We explore this question by analyzing different uses of Facebookâone of the forefront services provided through Free Basicsâand their relation to information technology (IT) identity and social capital. We find that, while issues and concerns surrounding Free Basics existâe.g. restrictions on participants\u27 choices in accessing and using information, possible privacy risks, and potential societal costsâthere is room for positive aspects in broader use of Facebook, despite its potential pitfalls. We suggest ways to analyze both the contradictions and contributions of Free Basics to individual and community development, and examine implications for ICTD and sustainable development in general
Immune DNA signature of T-cell infiltration in breast tumor exomes.
Tumor infiltrating lymphocytes (TILs) have been associated with favorable prognosis in multiple tumor types. The Cancer Genome Atlas (TCGA) represents the largest collection of cancer molecular data, but lacks detailed information about the immune environment. Here, we show that exome reads mapping to the complementarity-determining-region 3 (CDR3) of mature T-cell receptor beta (TCRB) can be used as an immune DNA (iDNA) signature. Specifically, we propose a method to identify CDR3 reads in a breast tumor exome and validate it using deep TCRB sequencing. In 1,078 TCGA breast cancer exomes, the fraction of CDR3 reads was associated with TILs fraction, tumor purity, adaptive immunity gene expression signatures and improved survival in Her2+ patients. Only 2/839 TCRB clonotypes were shared between patients and none associated with a specific HLA allele or somatic driver mutations. The iDNA biomarker enriches the comprehensive dataset collected through TCGA, revealing associations with other molecular features and clinical outcomes
Facebookâs âFree Basicsâ: For or against community development?
A recent discussion on a prominent community informatics (CI) listserv revealed arguments for and against the Facebookâs Free Basics platform among researchers in the field. To continue and enrich the conversation, this study first examines the contrasting stances revealed in the CI listserv discussion and derives the CI researchersâ major concerns about the platform. Under the light of these concerns, we then explore the nature of Facebookâs Free Basics in relation to community development through analysis of one of the forefront services that Free Basics offers, i.e., Facebook. Specifically, we examine relationships between uses of Facebook and information technology (IT) identity formation and social capital. We argue that although projects operated by private companies may possess potential for supporting community development, much consideration is needed in embracing the technology solutions due to the risks and restrictions they can impose on its users. We also suggest the CI researchers to open the next round of discussion regarding ways to thoroughly assess possible flaws of Free Basics and help users of the platform make more informed decisions. IT identity is a new theory that can help shed new light on the challenges of using platforms such as Free Basics and their contribution to community development
Hydrogen Bond Disruption in DNA Base Pairs from 14C Transmutation
Recent ab initio molecular dynamics simulations have shown that radioactive carbon does not normally fragment DNA bases when it decays. Motivated by this finding, density functional theory and Bader analysis have been used to quantify the effect of C â N transmutation on hydrogen bonding in DNA base pairs. We find that 14C decay has the potential to significantly alter hydrogen bonds in a variety of ways including direct proton shuttling (thymine and cytosine), thermally activated proton shuttling (guanine), and hydrogen bond breaking (cytosine). Transmutation substantially modifies both the absolute and relative strengths of the hydrogen bonding pattern, and in two instances (adenine and cytosine), the density at the critical point indicates development of mild covalent character. Since hydrogen bonding is an important component of Watson-Crick pairing, these 14C-induced modifications, while infrequent, may trigger errors in DNA transcription and replication
Ultraspinning instability of rotating black holes
Rapidly rotating Myers-Perry black holes in d>5 dimensions were conjectured
to be unstable by Emparan and Myers. In a previous publication, we found
numerically the onset of the axisymmetric ultraspinning instability in the
singly-spinning Myers-Perry black hole in d=7,8,9. This threshold signals also
a bifurcation to new branches of axisymmetric solutions with pinched horizons
that are conjectured to connect to the black ring, black Saturn and other
families in the phase diagram of stationary solutions. We firmly establish that
this instability is also present in d=6 and in d=10,11. The boundary conditions
of the perturbations are discussed in detail for the first time and we prove
that they preserve the angular velocity and temperature of the original
Myers-Perry black hole. This property is fundamental to establish a
thermodynamic necessary condition for the existence of this instability in
general rotating backgrounds. We also prove a previous claim that the
ultraspinning modes cannot be pure gauge modes. Finally we find new
ultraspinning Gregory-Laflamme instabilities of rotating black strings and
branes that appear exactly at the critical rotation predicted by the
aforementioned thermodynamic criterium. The latter is a refinement of the
Gubser-Mitra conjecture.Comment: 38 pages, 6 figures, 1 tabl
Conserved charges for gravity with locally AdS asymptotics
A new formula for the conserved charges in 3+1 gravity for spacetimes with
local AdS asymptotic geometry is proposed. It is shown that requiring the
action to have an extremum for this class of asymptotia sets the boundary term
that must be added to the Lagrangian as the Euler density with a fixed weight
factor. The resulting action gives rise to the mass and angular momentum as
Noether charges associated to the asymptotic Killing vectors without requiring
specification of a reference background in order to have a convergent
expression. A consequence of this definition is that any negative constant
curvature spacetime has vanishing Noether charges. These results remain valid
in the limit of vanishing cosmological constant.Comment: 5 pages, 2 Columns, revtex. Last version for Phys. Rev. Let
Recommended from our members
Understanding complementary basic education in Ghana
No description supplie
Sub-Meter Tree Height Mapping of California using Aerial Images and LiDAR-Informed U-Net Model
Tree canopy height is one of the most important indicators of forest biomass,
productivity, and species diversity, but it is challenging to measure
accurately from the ground and from space. Here, we used a U-Net model adapted
for regression to map the canopy height of all trees in the state of California
with very high-resolution aerial imagery (60 cm) from the USDA-NAIP program.
The U-Net model was trained using canopy height models computed from aerial
LiDAR data as a reference, along with corresponding RGB-NIR NAIP images
collected in 2020. We evaluated the performance of the deep-learning model
using 42 independent 1 km sites across various forest types and landscape
variations in California. Our predictions of tree heights exhibited a mean
error of 2.9 m and showed relatively low systematic bias across the entire
range of tree heights present in California. In 2020, trees taller than 5 m
covered ~ 19.3% of California. Our model successfully estimated canopy heights
up to 50 m without saturation, outperforming existing canopy height products
from global models. The approach we used allowed for the reconstruction of the
three-dimensional structure of individual trees as observed from nadir-looking
optical airborne imagery, suggesting a relatively robust estimation and mapping
capability, even in the presence of image distortion. These findings
demonstrate the potential of large-scale mapping and monitoring of tree height,
as well as potential biomass estimation, using NAIP imagery.Comment: 29 pages, 9 figures, submitted to Remote Sensing in Ecology and
Conservation (RSEC
The Shape of Galaxy Cluster Dark Matter Haloes: Systematics of Its Imprint on Cluster Gas, and Comparison to Observations
(Abridged) We study predictions for galaxy cluster observables that can test
the statistics of dark matter halo shapes expected in a flat LCDM universe. We
present a simple analytical model for the prediction of cluster-scale X-ray
observations, approximating clusters as isothermal systems in hydrostatic
equilibrium, and dark matter haloes as ellipsoids with uniform axial ratios. We
test the model against high-resolution, hydrodynamic cluster simulations to
gauge its reliability. We find that this simple prescription does a good job of
predicting the distribution of cluster X-ray ellipticities compared to the
simulations as long as one focuses on cluster regions that are less sensitive
to recent mergers. Based on this simple model, the distribution of cluster-size
halo shapes expected in the concordance LCDM cosmology implies an X-ray
ellipticity distribution with a mean of 0.32 +- 0.01 and a scatter of 0.14 +-
0.01 for the mass range (1-4)x10^{14} Msun/h. We find it important to include
the mass dependence of halo shape to make comparisons to observational samples
that contain many, very massive clusters. We analyse the systematics of four
observational samples of cluster ellipticities and find that our results are
statistically compatible with observations. In particular, we find remarkably
good agreement between two recent ROSAT samples and LCDM predictions that DO
NOT include gas cooling. We also test how well our analytical model can predict
Sunyaev-Zel'dovich decrement maps and find that it is less successful although
still useful; the model does not perform as well as a function of flux level in
this case because of the changing triaxiality of dark matter haloes as a
function of radial distance. Both this effect and the changing alignment of
isodensity shells of dark matter haloes leave an imprint on cluster gas...Comment: 16 pages, 9 figures; corrected typo (no result affected) submitted to
MNRA
- âŠ