48 research outputs found
Accelerating Growth and Size-dependent Distribution of Human Activities Online
Research on human online activities usually assumes that total activity
increases linearly with active population , that is, . However, we find examples of systems where total
activity grows faster than active population. Our study shows that the power
law relationship is in fact ubiquitous in
online activities such as micro-blogging, news voting and photo tagging. We
call the pattern "accelerating growth" and find it relates to a type of
distribution that changes with system size. We show both analytically and
empirically how the growth rate associates with a scaling parameter
in the size-dependent distribution. As most previous studies explain
accelerating growth by power law distribution, the model of size-dependent
distribution is novel and worth further exploration.Comment: 6 pages, 2 figure
Separable and non-separable multi-field inflation and large non-Gaussianity
In this paper we provide a general framework based on formalism to
estimate the cosmological observables pertaining to the cosmic microwave
background radiation for non-separable potentials, and for generic \emph{end of
inflation} boundary conditions. We provide analytical and numerical solutions
to the relevant observables by decomposing the cosmological perturbations along
the curvature and the isocurvature directions, \emph{instead of adiabatic and
entropy directions}. We then study under what conditions large bi-spectrum and
tri-spectrum can be generated through phase transition which ends inflation. In
an illustrative example, we show that large and
can be obtained for the case of separable and
non-separable inflationary potentials.Comment: 21 pages, 6 figure
Similarities and Differences in the Fermiology of Kagome Metals AVSb (A=K, Rb, Cs) Revealed by Shubnikov-de Haas Oscillations
Materials with AVSb (A=K, Rb, Cs) stoichiometry are recently
discovered kagome superconductors with the electronic structure featuring a
Dirac band, van Hove singularities and flat bands. These systems undergo
anomalous charge-density-wave (CDW) transitions at ~80-100 K,
resulting in the reconstruction of the Fermi surface from the pristine phase.
Although comprehensive investigations of the electronic structure via quantum
oscillations (QOs) have been performed on the sister compounds CsVSb
and RbVSb, a detailed QO study of KVSb is so far absent. Here,
we report the Shubnikov-de Haas QO study in KVSb. We resolve a large
number of new frequencies with the highest frequency of 2202 T (occupying ~54%
of the Brillouin zone area in the - plane). The Lifshitz-Kosevich
analysis further gives relatively small cyclotron effective masses, and the
angular dependence study reveals the two-dimensional nature of the frequencies
with a sufficient signal-to-noise ratio. Finally, we compare the QO spectra for
all three AVSb compounds collected under the same conditions, enabling
us to point out the similarities and differences across these systems. Our
results fill in the gap of the QO study in KVSb and provide valuable
data to understand the band structure of all three members of AVSb.Comment: 8 pages, 4 figure
Nodeless superconductivity in kagome metal CsVSb with and without time reversal symmetry breaking
The kagome metal CsVSb features an unusual competition between
the charge-density-wave (CDW) order and superconductivity. Evidence for
time-reversal symmetry breaking (TRSB) inside the CDW phase has been
accumulating. Hence, the superconductivity in CsVSb emerges from a
TRSB normal state, potentially resulting in an exotic superconducting state. To
reveal the pairing symmetry, we first investigate the effect of nonmagnetic
impurity. Our results show that the superconducting critical temperature is
insensitive to disorder, pointing to conventional -wave superconductivity.
Moreover, our measurements of the self-field critical current (),
which is related to the London penetration depth, also confirm conventional
-wave superconductivity with strong coupling. Finally, we measure
where the CDW order is removed by pressure and superconductivity emerges from
the pristine normal state. Our results show that -wave gap symmetry is
retained, providing strong evidence for the presence of conventional -wave
superconductivity in CsVSb irrespective of the presence of the TRSBComment: 8 pages, 4 figures. Nano Letters (in press
Multifactorial anticancer effects of digalloyl-resveratrol encompass apoptosis, cell-cycle arrest, and inhibition of lymphendothelial gap formation in vitro
BACKGROUND: Digalloyl-resveratrol (di-GA) is a synthetic compound aimed to combine the biological effects of the plant polyhydroxy phenols gallic acid and resveratrol, which are both radical scavengers and cyclooxygenase inhibitors exhibiting anticancer activity. Their broad spectrum of activities may probably be due to adjacent free hydroxyl groups.
METHODS: Protein activation and expression were analysed by western blotting, deoxyribonucleoside triphosphate levels by HPLC, ribonucleotide reductase activity by 14 C-cytidine incorporation into nascent DNA and cell-cycle distribution by FACS. Apoptosis was measured by Hoechst 33258/propidium iodide double staining of nuclear chromatin and the formation of gaps into the lymphendothelial barrier in a three-dimensional co-culture model consisting of MCF-7 tumour cell spheroids and human lymphendothelial monolayers.
RESULTS: In HL-60 leukaemia cells, di-GA activated caspase 3 and dose-dependently induced apoptosis. It further inhibited cell-cycle progression in the G1 phase by four different mechanisms: rapid downregulation of cyclin D1, induction of Chk2 with simultaneous downregulation of Cdc25A, induction of the Cdk-inhibitor p21(Cip/Waf) and inhibition of ribonucleotide reductase activity resulting in reduced dCTP and dTTP levels. Furthermore, di-GA inhibited the generation of lymphendothelial gaps by cancer cell spheroid-secreted lipoxygenase metabolites. Lymphendothelial gaps, adjacent to tumour bulks, can be considered as gates facilitating metastatic spread.
CONCLUSION: These data show that di-GA exhibits three distinct anticancer activities: induction of apoptosis, cell-cycle arrest and disruption of cancer cell-induced lymphendothelial disintegration. British Journal of Cancer (2010) 102, 1361-1370. doi:10.1038/sj.bjc.6605656 www.bjcancer.com (C) 2010 Cancer Research U
Arbuscular mycorrhizal colonisation of roots of grass species differing in invasiveness
Recent research indicates that the soil microbial community, particularly arbuscular mycorrhizal
fungi (AMF), can influence plant invasion in several ways. We tested if 1) invasive species are
colonised by AMF to a lower degree than resident native species, and 2) AMF colonisation of native
plants is lower in a community inhabited by an invasive species than in an uninvaded resident
community. The two tests were run in semiarid temperate grasslands on grass (Poaceae) species,
and the frequency and intensity of mycorrhizal colonisation, and the proportion of arbuscules and
vesicles in plant roots have been measured. In the first test, grasses representing three classes of
invasiveness were included: invasive species, resident species becoming abundant upon
disturbance, and non-invasive native species. Each class contained one C3 and one C4 species. The
AMF colonisation of the invasive Calamagrostis epigejos and Cynodon dactylon was consistently
lower than that of the non-invasive native Chrysopogon gryllus and Bromus inermis, and contained
fewer arbuscules than the post-disturbance dominant resident grasses Bothriochloa ischaemum and
Brachypodium pinnatum. The C3 and C4 grasses behaved alike despite their displaced phenologies
in these habitats. The second test compared AMF colonisation for sand grassland dominant grasses
Festuca vaginata and Stipa borysthenica in stands invaded by either C. epigejos or C. dactylon, and
in the uninvaded natural community. Resident grasses showed lower degree of AMF colonisation in the invaded stand compared to the uninvaded natural community with F. vaginata responding so to
both invaders, while S. borysthenica responding to C. dactylon only. These results indicate that
invasive grasses supposedly less reliant on AMF symbionts have the capacity of altering the soil
mycorrhizal community in such a way that resident native species can establish a considerably
reduced extent of the beneficial AMF associations, hence their growth, reproduction and ultimately
abundance may decline. Accumulating evidence suggests that such indirect influences of invasive
alien plants on resident native species mediated by AMF or other members of the soil biota is probably more the rule than the exception
Ocorrência de fungos endofíticos "dark septate" em raízes de Oryza glumaepatula na Amazônia
Influence of edapho-climatic factors on the sporulation and colonization of arbuscular mycorrhizal fungi in two Amazonian native fruit species
Arbuscular mycorrhizal fungi (AMF) colonization and spore numbers in the rhizosphere of two fruit species, Paullinia cupana Mart. and Theobroma grandiflorum Schum., growing in a terra firme ecosystem in Central Amazonia were studied from August 1998 to May 2000. Climatic and edaphic factors were also determined to investigate their influence on mycorrhizal variables. Soil pH, Al, Mn and effective cation exchange capacity exhibited seasonal variations during the investigation period. Temporal variations in mycorrhizal colonization levels and spore numbers occurred, indicating seasonality. Moreover, the patterns of mycorrhizal colonization levels and spore numbers for both host species were similar during the studied period. Mycorrhizal variables were related to climatic and edaphic factors, however, the intensity and type of influence of climatic and soil characteristics on AMF development tended to vary with the season and host plant species in Central Amazonia conditions
A Service-Based Selfish Routing for Mobile Social Networks
Routing in mobile social networks is a challenging task due to the characteristic of intermittent connectivity, especially when the nodes behave selfishly in real world. Selfish behaviors of node always influence its altruism to provide forwarding service for others and degrade network performance strongly. In this paper, to address the selfishness problem in MSNs, we propose a service-based selfish routing protocol, SSR. When making forwarding decision, SSR employ user altruism and the amount of service that the relay nodes provide. User altruism is determined by the social selfishness and the individual selfishness. The services include pairwise services and social services, which is also considered as the incentives to stimulate node to be more cooperative. The more services the node provides, the more chance the node has to be served. The node with higher altruism and fewer services is the preferred relay node. Simulation results show SSR achieves better performance when the user altruism is low and demonstrate the effectiveness of the service-based scheme.Published versio