6,004 research outputs found
On the power divergence in quasi gluon distribution function
Recent perturbative calculation of quasi gluon distribution function at
one-loop level shows the existence of extra linear ultraviolet divergences in
the cut-off scheme. We employ the auxiliary field approach, and study the
renormalization of gluon operators. The non-local gluon operator can mix with
new operators under renormalization, and the linear divergences in quasi
distribution function can be into the newly introduced operators. After
including the mixing, we find the improved quasi gluon distribution functions
contain only logarithmic divergences, and thus can be used to extract the gluon
distribution in large momentum effective theory.Comment: 18 pages, 10 figures. Published version in JHE
Real-time Bidding for Online Advertising: Measurement and Analysis
The real-time bidding (RTB), aka programmatic buying, has recently become the
fastest growing area in online advertising. Instead of bulking buying and
inventory-centric buying, RTB mimics stock exchanges and utilises computer
algorithms to automatically buy and sell ads in real-time; It uses per
impression context and targets the ads to specific people based on data about
them, and hence dramatically increases the effectiveness of display
advertising. In this paper, we provide an empirical analysis and measurement of
a production ad exchange. Using the data sampled from both demand and supply
side, we aim to provide first-hand insights into the emerging new impression
selling infrastructure and its bidding behaviours, and help identifying
research and design issues in such systems. From our study, we observed that
periodic patterns occur in various statistics including impressions, clicks,
bids, and conversion rates (both post-view and post-click), which suggest
time-dependent models would be appropriate for capturing the repeated patterns
in RTB. We also found that despite the claimed second price auction, the first
price payment in fact is accounted for 55.4% of total cost due to the
arrangement of the soft floor price. As such, we argue that the setting of soft
floor price in the current RTB systems puts advertisers in a less favourable
position. Furthermore, our analysis on the conversation rates shows that the
current bidding strategy is far less optimal, indicating the significant needs
for optimisation algorithms incorporating the facts such as the temporal
behaviours, the frequency and recency of the ad displays, which have not been
well considered in the past.Comment: Accepted by ADKDD '13 worksho
Gluon quasidistribution function at one loop
We study the unpolarized gluon quasidistribution function in the nucleon at
one loop level in the large momentum effective theory. For the quark
quasidistribution, power law ultraviolet divergences arise in the cut-off
scheme and an important observation is that they all are subjected to Wilson
lines. However for the gluon quasidistribution function, we first point out
that the linear ultraviolet divergences also exist in the real diagram which is
not connected to any Wilson line. We then study the one loop corrections to
parton distribution functions in both cut-off scheme and dimensional
regularization to deal with the ultraviolet divergences. In addition to the
ordinary quark and gluon distributions, we also include the quark to gluon and
gluon to quark splitting diagrams. The complete one-loop matching factors
between the quasi and light cone parton distribution functions are presented in
the cut-off scheme. We derive the evolution equation for quasi parton
distribution functions, and find that the evolution kernels are identical
to the DGLAP evolution kernels.Comment: 26 pages,8 figures;accepted by Eur.Phys.J
Effects of Hypoxic Conditions on Skeletal Myoblasts
Hypoxic injury in skeletal muscle occurs in response to musculoskeletal traumas, diseases and following reconstructive and transplantation surgeries. However, the molecular mechanisms responsible for hypoxic injury in skeletal myoblasts have yet to be fully investigated. Understanding of these molecular mechanisms would identify potential therapeutic targets. Herein, we have determined that treatment with cobalt chloride (CoCl2, a hypoxia mimicking agent) first leads to an inhibition of proliferation followed by a decrease in the number of viable myoblasts over time. FACS analysis revealed a marked increase in G2/M arrest after 24 hours of treatment. We next assessed PARP cleavage, a well-known hallmark of apoptosis, and detected cleavage after 48 hours, suggesting apoptosis as a mechanism contributing to myoblast death. Since we have recently determined that PUMA (p53 up-regulated modulator of apoptosis) plays a critical role in the apoptosis associated with skeletal myoblast differentiation, we assessed the level of PUMA expression in response to CoCl2 treatment and documented an increase in PUMA protein and mRNA. We did find an increase in p53 expression suggesting that this transcription factor is responsible for the increased expression of PUMA. Moreover, this increase in PUMA expression occurs under condition of eIF2a phosphorylation, which implies the possibility of IRES (Internal Ribosome Entry Site)-mediated regulation of PUMA expression under hypoxic conditions. Indeed, actinomycin D induced abrogation of the increase in PUMA mRNA did not prevent the increase in PUMA protein. In skeletal myoblasts, the processes of differentiation and apoptosis are coordinately regulated during myogenesis and muscle regeneration and this coordinated regulation is mediated by the transcription factor MyoD. Thus, we next assessed the effect of CoCl2 treatment on MyoD expression and documented decreased levels of MyoD protein and mRNA. Although we have also determined that the decrease in mRNA was not a consequence of a shortened half-life suggesting an effect on SRF, the transcription factor controlling MyoD expression, we were unable to detect a change in SRF expression as a consequence of CoCl2 treatment. Future experiments will assess the activation of SRF
Counting linearly polarized gluons with lattice QCD
We outline an approach to calculate the transverse-momentum-dependent
distribution of linearly polarized gluons inside an unpolarized hadron on the
lattice with the help of large momentum effective theory. To achieve this
purpose, we propose calculating a Euclidean version of the degree of
polarization for a fast-moving hadron on the lattice, which is ultraviolet
finite, and no soft function subtraction is needed. It indicates a practical
way to explore the distribution of the linearly polarized gluons in a proton
and the linearly polarized gluon effects in hadron collisions on the lattice.Comment: 6 pages, 1 figure. To match the published versio
Heavy quark expansion for heavy-light light-cone operators
We generalize the celebrated heavy quark expansion to nonlocal QCD operators.
By taking nonlocal heavy-light current on the light-cone as an example, we
confirm that the collinear singularities are common between QCD operator and
the corresponding operator in heavy quark effective theory (HQET), at the
leading power of expansion. Based on a perturbative calculation in
operator form at one-loop level, a factorization formula linking QCD and HQET
operators is investigated and the matching coefficient is determined. The
matching between QCD and HQET light-cone distribution amplitudes (LCDAs) as
well as other momentum distributions of hadron can be derived as a consequence.Comment: 6 pages. Results slightly modified, references updated. Published in
Physical Review
Heavy Quark Expansion for Heavy-Light Light-Cone Operators
We generalize the celebrated heavy quark expansion to nonlocal QCD operators. By taking nonlocal heavy-light current on the light-cone as an example, we confirm that the collinear singularities are common between QCD operator and the corresponding operator in heavy quark effective theory (HQET), at the leading power of 1/M expansion. Based on a perturbative calculation in operator form at one-loop level, a factorization formula linking QCD and HQET operators is investigated and the matching coefficient is determined. The matching between QCD and HQET light-cone distribution amplitudes (LCDAs) as well as other momentum distributions of hadron can be derived as a consequence
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