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 $P^z$ evolution equation for quasi parton distribution functions, and find that the $P^z$ evolution kernels are identical to the DGLAP evolution kernels.Comment: 26 pages,8 figures;accepted by Eur.Phys.J

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.Comment: 6 pages. Results slightly modified, references updated. Published in Physical Review

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