169 research outputs found
Time-Varying Gravitomagnetism
Time-varying gravitomagnetic fields are considered within the linear
post-Newtonian approach to general relativity. A simple model is developed in
which the gravitomagnetic field of a localized mass-energy current varies
linearly with time. The implications of this temporal variation of the source
for the precession of test gyroscopes and the motion of null rays are briefly
discussed.Comment: 10 pages; v2: slightly expanded version accepted for publication in
Class. Quantum Gra
Nitrogen deprivation induces triacylglycerol accumulation, drug tolerance and hypervirulence in mycobacteria.
Mycobacteria share with other actinomycetes the ability to produce large quantities of triacylglycerol (TAG), which accumulate as intracytoplasmic lipid inclusions (ILI) also known as lipid droplets (LD). Mycobacterium tuberculosis (M. tb), the etiologic agent of tuberculosis, acquires fatty acids from the human host which are utilized to synthesize TAG, subsequently stored in the form of ILI to meet the carbon and nutrient requirements of the bacterium during long periods of persistence. However, environmental factors governing mycobacterial ILI formation and degradation remain poorly understood. Herein, we demonstrated that in the absence of host cells, carbon excess and nitrogen starvation promote TAG accumulation in the form of ILI in M. smegmatis and M. abscessus, used as surrogate species of M. tb. Based on these findings, we developed a simple and reversible in vitro model to regulate ILI biosynthesis and hydrolysis in mycobacteria. We also showed that TAG formation is tgs1 dependent and that lipolytic enzymes mediate TAG breakdown. Moreover, we confirmed that the nitrogen-deprived and ILI-rich phenotype was associated with an increased tolerance towards several drugs used for treating mycobacterial infections. Importantly, we showed that the presence of ILI substantially enhanced the bacterial burden and granuloma abundance in zebrafish embryos infected with lipid-rich M. abscessus as compared to embryos infected with lipid-poor M. abscessus, suggesting that ILI are actively contributing to mycobacterial virulence and pathogenesis
Accurate light-time correction due to a gravitating mass
This work arose as an aftermath of Cassini's 2002 experiment \cite{bblipt03},
in which the PPN parameter was measured with an accuracy
and found consistent with the prediction
of general relativity. The Orbit Determination Program (ODP) of
NASA's Jet Propulsion Laboratory, which was used in the data analysis, is based
on an expression for the gravitational delay which differs from the standard
formula; this difference is of second order in powers of -- the sun's
gravitational radius -- but in Cassini's case it was much larger than the
expected order of magnitude , where is the ray's closest approach
distance. Since the ODP does not account for any other second-order terms, it
is necessary, also in view of future more accurate experiments, to
systematically evaluate higher order corrections and to determine which terms
are significant. Light propagation in a static spacetime is equivalent to a
problem in ordinary geometrical optics; Fermat's action functional at its
minimum is just the light-time between the two end points A and B. A new and
powerful formulation is thus obtained. Asymptotic power series are necessary to
provide a safe and automatic way of selecting which terms to keep at each
order. Higher order approximations to the delay and the deflection are
obtained. We also show that in a close superior conjunction, when is much
smaller than the distances of A and B from the Sun, of order , say, the
second-order correction has an \emph{enhanced} part of order , which
corresponds just to the second-order terms introduced in the ODP. Gravitational
deflection of the image of a far away source, observed from a finite distance
from the mass, is obtained to .Comment: 4 figure
Gravitational bending of light by planetary multipoles and its measurement with microarcsecond astronomical interferometers
General relativistic deflection of light by mass, dipole, and quadrupole
moments of gravitational field of a moving massive planet in the Solar system
is derived. All terms of order 1 microarcsecond are taken into account,
parametrized, and classified in accordance with their physical origin. We
calculate the instantaneous patterns of the light-ray deflections caused by the
monopole, the dipole and the quadrupole moments, and derive equations
describing apparent motion of the deflected position of the star in the sky
plane as the impact parameter of the light ray with respect to the planet
changes due to its orbital motion. The present paper gives the physical
interpretation of the observed light-ray deflections and discusses the
observational capabilities of the near-future optical (SIM) and radio (SKA)
interferometers for detecting the Doppler modulation of the radial deflection,
and the dipolar and quadrupolar light-ray bendings by the Jupiter and the
Saturn.Comment: 33 pages, 10 figures, accepted to Phys. Rev.
Tubectomy of Pregnant and Non-pregnant Female Balinese Macaques (Macaca Fascicularis) With Post-operative Monitoring
peer reviewedWorldwide, primates, and humans increasingly share habitats and often enter in conflict when primates thrive in human-dominated environments, calling for special management measures. Reproductive control is increasingly used to manage population growth but very few monitoring data are available. Therefore, the efficiency and implications of such programs require a careful examination. In the context of a contraception program in wild female long-tailed macaques in Ubud, Bali, conducted over four successive campaigns between 2017 and 2019, including 140 females (i.e., 41.9% of the reproductive females of the population in 2019), modifications of an endoscopic tubectomy procedure, a permanent sterilization method, clinical evaluation of this method, and the post-operative monitoring results of the neutered females after release are described. This surgical approach was applicable for pregnant females: 28.6% of the treated females were pregnant at the time of the surgery. The procedure used a single lateral port to reach and cauterize both oviducts in non-pregnant as well as in early to mid-term pregnant females. Pregnant females nearer to term required a second lateral port to access both oviducts masked by the size of the gravid uterus. Moreover, bipolar thermocauterization was utilized successfully without resection to realize the tubectomy. The average duration of the laparoscopic surgery was 14 min for non-pregnant females and 22 min for pregnant females. Animals were released 3 h 22 min in average following their capture. This short holding time, recommended for free-ranging primates, was made possible by the minimal invasiveness of the sterilization approach. A laparoscopic post-operative evaluation conducted on two patients during the following campaign confirmed that the oviducts were definitely disrupted and no longer patent. Moreover, no new pregnancies in sterilized females were recorded during the 3-year observation period. The survival rate of the treated females 6 months after sterilization was high (96.3%) with no major post-operative complications clinically recorded. Among females that were pregnant during surgery, 81.1% were confirmed to experience term delivery. This study demonstrates the safety and efficiency of endoscopic tubectomy, even for pregnant females, as a mean of wild macaques' population control
Augmented Reality: What Motivates Late Millennials towards Fashion Mobile Apps?
Generation Z is expected to be a dominant demographic and economic group. Cyber-waviness,
constant reliance on smart devices that allows them to be always connected are among some of
their intrinsic characteristics. The combination of this reality with the ever-changing
technological environment is compelling retailers to reshape their business strategies, to meet
this group desires and expectations and to foster their engagement. Augmented reality (AR) is
emerging as a technological solution that pleases both consumers and retailers. This paper aims
to answer two main questions: (1) How does generation Z evaluate an AR experience? (2)
Which attributes/benefits do they value or not during an AR experience? Drawing on a
qualitative methodology – content analysis of 34 interviewees – we discuss six main
dimensions the potential customer value of the relationship between them and AR experiences
under retailer context.info:eu-repo/semantics/publishedVersio
<i>Gaia</i> Data Release 1. Summary of the astrometric, photometric, and survey properties
Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7.
Aims. A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release.
Methods. The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue.
Results. Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the HIPPARCOS and Tycho-2 catalogues – a realisation of the Tycho-Gaia Astrometric Solution (TGAS) – and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of ∼3000 Cepheid and RR-Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr−1 for the proper motions. A systematic component of ∼0.3 mas should be added to the parallax uncertainties. For the subset of ∼94 000 HIPPARCOS stars in the primary data set, the proper motions are much more precise at about 0.06 mas yr−1. For the secondary astrometric data set, the typical uncertainty of the positions is ∼10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to ∼0.03 mag over the magnitude range 5 to 20.7.
Conclusions. Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature five-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data
Augmenting the Eye of the Beholder: Exploring the Strategic Potential of Augmented Reality to Enhance Online Service Experiences
Driven by the proliferation of augmented reality (AR) technologies, many firms are pursuing a strategy of service augmentation to enhance customers’ online service experiences. Drawing on situated cognition theory, the authors show that AR - based service augmentation enhances customer value perceptions by simultaneously providing simulated physical control and environmental embedding. The resulting authentic situated experience, manifested in a feeling of spatial presence, funct ions as a mediator and also predicts customer decision comfort. Furthermore, the effect of spatial presence on utilitarian value perceptions is greater for customers who are disposed toward verbal rather than visual information processing, and the positive effect on decision comfort is attenuated by customers’ privacy concerns
Characterization of Spontaneous Bone Marrow Recovery after Sublethal Total Body Irradiation: Importance of the Osteoblastic/Adipocytic Balance
Many studies have already examined the hematopoietic recovery after irradiation but paid with very little attention to the bone marrow microenvironment. Nonetheless previous studies in a murine model of reversible radio-induced bone marrow aplasia have shown a significant increase in alkaline phosphatase activity (ALP) prior to hematopoietic regeneration. This increase in ALP activity was not due to cell proliferation but could be attributed to modifications of the properties of mesenchymal stem cells (MSC). We thus undertook a study to assess the kinetics of the evolution of MSC correlated to their hematopoietic supportive capacities in mice treated with sub lethal total body irradiation. In our study, colony-forming units – fibroblasts (CFU-Fs) assay showed a significant MSC rate increase in irradiated bone marrows. CFU-Fs colonies still possessed differentiation capacities of MSC but colonies from mice sacrificed 3 days after irradiation displayed high rates of ALP activity and a transient increase in osteoblastic markers expression while pparγ and neuropilin-1 decreased. Hematopoietic supportive capacities of CFU-Fs were also modified: as compared to controls, irradiated CFU-Fs significantly increased the proliferation rate of hematopoietic precursors and accelerated the differentiation toward the granulocytic lineage. Our data provide the first evidence of the key role exerted by the balance between osteoblasts and adipocytes in spontaneous bone marrow regeneration. First, (pre)osteoblast differentiation from MSC stimulated hematopoietic precursor's proliferation and granulopoietic regeneration. Then, in a second time (pre)osteoblasts progressively disappeared in favour of adipocytic cells which down regulated the proliferation and granulocytic differentiation and then contributed to a return to pre-irradiation conditions
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