This is a writeup of my lectures given at the International Workshop on Frontiers of High Energy Physics, held at CCAST, Beijing, China during July 2-10. I discuss some basic experimental techniques for studying the Top quark and Higgsboson at the Tevatron, and review some recent results from CDF and D0 and their future prospects.

Atmospheric rivers (ARs) are filaments of enhanced water vapor transport in the atmosphere. Globally, ARs play a key role in the meridional moisture transport. Regionally,ARs can either serve as freshwater suppliers or culprits behind many of the weather hazards. ARs and their impacts have been studied extensively. However, what controls the variability of ARs on different time scales remains largely unknown. In particular, further studies are especially needed to better understand the relative role of circulation (dynamic) variability versus moisture (thermodynamic) variability, internal variability versus sea surface temperature (SST)/ sea ice variability and anthropogenic forcing versus internal variability originated from SST/sea ice variability in controlling the variability of ARs and their associated precipitation on different time scales. In addition, reanalyses have long been used as proxies of observations in AR studies. Yet, the representation of ARs and their associated precipitation in reanalyses remain unknown. Although satellite observations have also been used to study ARs, previous satellite-based AR studies used only the moisture component (integrated water vapor or IWV) to detect ARs. While ARs have been defined as filaments of enhanced moisture transport in the atmosphere, detecting ARs with only the moisture field would inevitably run the risk of detecting those filamentary features with high moisture content, but relatively weak transport component. In this dissertation, we will address the research gaps above from five different angles. First, we investigate the relative role of SST/sea ice versus internal variability in driving the interannual variability of winter AR activities over the North Hemisphere. We show that, while both SST/sea ice and internal variability play roles in driving the interannual AR variability, their roles differ across ocean basins. Over the North Pacific, SST/sea ice variability exerts substantially stronger control on the AR variability compared to interval variability. However, both SST/sea ice and internal variability play comparable roles in modulating the AR variability over the North Atlantic. Second, on longer time scale, we discover that ARs over the Southern Hemisphere have been shifting poleward in the past four decades. Using a simple scaling method, we find that this poleward shift in the ARs is mostly driven by the poleward shift of the westerly jet (dynamic) while the contribution from the changes in the moisture field is relatively minor. Using two ensembles from the Community Earth System Model (CESM), one with fully coupled oceans and another one driven by observed SST/sea ice, we show that anthropogenic forcing is mainly responsible for the observed poleward shift. However, the negative phase of Interdecadal Pacific Oscillation (IPO) in recent decades also further drives the poleward shift in ARs. Third, ARs are expected to change under a warmer climate. However, the AR response to warming is determined by numerous factors. Two of the most prominent factors are the warming of the tropical upper troposphere, which can drive the poleward shift of the westerly jet, and the amplified warming of the polar regions, which can drive the equatorward shift of the westerly jet. Using nine models participated in the Polar Amplification Model Intercomparison Project (PAMIP), we investigate how Arctic Amplification and its associated sea ice loss would affect the boreal winter AR activities over the Northern Hemisphere. We find that, in response to Arctic sea ice loss, ARs extend northeastward over North Pacific and shift equatorward over North Atlantic. We further demonstrate that these response patterns are mostly determined by the responses in the circulation. Fourth, using a moisture budget approach, the relative contribution of dynamic change versus thermodynamic change to the intensification of extreme precipitation along the North American West Coast (predominantly driven by ARs) is also quantified. We show the intensification of the extreme precipitation along the North American West Coast is mostly driven by the increase in moisture while the contribution from the dynamic change is minor. Lastly, we develop a novel method to detect ARs in satellite observations using both IWV and wind information based on the geostrophic winds. Using this method, we create satellite-based AR statistics and use these statistics to evaluate the performance of seven commonly used reanalyses in representing ARs and their associated precipitation. We show that both satellite observation and reanalyses show high agreement with each other in representing the AR frequency distribution. In terms of AR precipitation, ARs in reanalyses tend to precipitate too lightly and too often. Our studies shed light on the mechanisms driving the variability of ARs across different time scales. These findings have important implications. First, given the more important role SST/sea ice variability in controlling the AR interannual variability, ARs in the North Pacific are likely more predictable than those over the North Atlantic. Better SST forecast can thus likely lead to better AR forecast along the North American West Coast. Second, on the interdecadal time scale, internal variability related to ocean processes still plays an important role in modulating AR variability. Internal variability should thus be taken into consideration when studying future AR response under warming. Third, our results indicate that the thermodynamic aspect of the AR and AR precipitation response is quite robust. We thus need to constrain the response in circulation to reduce the AR response uncertainty. Lastly, the finding that ARs in reanalyses tend to precipitate too often and too lightly directly questions the use of reanalysis-based precipitation in AR studies.

There is no clear path for building a particle accelerator at the energy frontier beyond the Large Hadron Collider (LHC). One option that is receiving attention is to use plasma wave wakefields driven by intense particle beams. Recent experiments conducted at the Stanford Linear Accelerator Center (SLAC) show that accelerating gradients in such wakefields in excess of 50 GeV/m can be sustained over meter scales. Based on this, a linear collider concept of staging one-meter long plasma cells together has been proposed. A facility at SLAC has been built to study the physics in one stage. In this dissertation we describe improvements and enhancements to a highly efficient simulation model for simulating current experiments at SLAC as well as parameters beyond the reach of current experiments. The model is the quasi-static particle-in-cell (PIC) code QuickPIC. A modified set of quasi-static field equations were developed, which reduced the number of predictor corrector iteration loops and an improved source deposit scheme was developed to reduce the parallel communication. These improvements led to a factor of 5 to 8 (depending on the simulation parameters) speedup compared with the previous set of field equations and deposition scheme. Several new modules were also added to QuickPIC, including the multiple field ionization and improved beam and plasma particle diagnostics. We also used QuickPIC to study the optimum plasma density for maximizing the acceleration field for fixed electron beam parameters. QuickPIC simulations were also used to study and design two-bunch PWFA experiments at SLAC including methods for mitigating the ionization-induced beam head erosion. The mitigation methods can enhance the energy gain in two-bunch PWFA experiments at SLAC by a factor of 10 for the same beam parameters. For beam parameters beyond SLAC but perhaps necessary for a future collider, QuickPIC was used to study how the ultra high electric fields of a tightly focused second electron bunch could lead to ion motion, which disrupts the focusing fields on the second bunch. The resulting nonlinearity in the transverse focusing force of the plasma wake will lead to emittance growth. We used QuickPIC to carry out the first fully self-consistent high resolution simulation on the effects of ion motion for PWFA linear collider problems. Preliminary results showed that the plasma-ion-motion-induced emittance growth was limited to less than a factor of 2. In addition to the electron beam driven PWFA, we also study how a short proton beam can excite a large plasma wake. Such short proton beams are currently not experimentally available. We therefore also study how long proton beams such as those at Fermi National Laboratory and CERN may drive a large plasma wake through a self-modulation instability. A linear theory for the self-modulation instability is presented under the wide beam limit. QuickPIC simulations show that the self-modulation of a long proton beam in a plasma may lead to the micro-bunching of the beam and excite a large plasma wake.

Background: Respondent-driven-sampling (RDS) has been recognized as a method for sampling from most hard-to-reach populations. Meanwhile, loss to follow up of the participants in follow up studies usually reduces the validity of the association measured in observational studies, and this problem cannot be overcame through data analysis.

Methods: In a cross sectional study in Nanjing city of Jiangsu province of China, 430 MSM were recruited including 9 seeds in 14 weeks of study period using RDS. Information regarding socio-demographic characteristics and sexual risk behavior were collected and testing was done for HIV and syphilis. Duration, completion, participant characteristics and the equilibrium of key factors were used for assessing feasibility of RDS. All the HIV negative participants were followed up at 6, 12 and 18 months to evaluate behavioral changes after counseling to reduce risk behaviors. Logistic regression was performed to identify the factors correlated with loss to follow up.

Results: In the study sample, adjusted HIV and syphilis prevalence were 6.6% and 14.6% respectively, whereas HIV incidence was 5.2 per 100 person-years. The incidence was 3.8 during six to 12 months, and 1.1 during 12 to 18 months. Although there was a tendency for recruitment within the same self-identified group, considerable cross-group recruitment was also seen. During the study period, the reported unprotected anal intercourse (UAI) significantly decreased from 60.9% to 42.9%. The proportion of participants who had one or no partner significantly increased from 40.9% to 48.0%. The study also found that some risk behaviors decreased between baseline and 12 months, followed by a slight increase between 12 and 18 months. In addition, loss to follow up for the MSM study in Nanjing was associated with younger age, small social network, lower education, and non-official residence in Jiangsu.

Conclusion: RDS was found to be a potential efficient and feasible sampling method for recruiting a diverse sample of MSM in a reasonable time. Reductions in UAI can be achieved through counseling and testing, but may wane over time. The factors correlated with loss-to-follow-up found in of our study may be helpful to increase the retention rate of future cohort studies.

HIV/AIDS population is known has higher risk of many malignant tumors, but cancer spectrum among HIV/AIDS population in China has not been reported, and risk factors of Kaposi Sarcoma (KS) among HIV-infected Chinese population remains unknown. This dissertation study describes the spectrum of malignancies among HIV/AIDS population in China, 2008-2011, and explores associated factors of KS both in the national HIV/AIDS cohort and in a hospital-based case-control study among HIV-infected Uyghur people in Xinjiang, China.

In part I, we used cohort data of national HIV/AIDS surveillance and information system during 2008-2011 to calculate standardized incidence rates (to China census 2010) and standardized incidence ratios (with China tumor registry 2008) of all reported cancers. Totally 3819 cancer reports were found from 399,451 subjects with followed-ups between 2008 and 2011. Higher risk was found in both AIDS-defining cancers (KS, lymphomas and cervical cancer) and non-AIDS-defining cancers (lung, liver, stomach, etc.) Comparing with western countries, HIV/AIDS population in China had lower risk of Kaposi Sarcoma, lymphomas, similar risk of female cervical cancer but higher risk of non-AIDS-defining cancers including lung, liver, and stomach cancers.

In part II, we analyzed risk factor of KS in the national HIV/AIDS cohort using Cox proportional hazard model. Being male (Hazard Ratio, HR 1.68, 95%CI 1.13-2.40), Uyghur ethnic (HR 5.30, 95%CI 3.68-7.64), HIV transmission route (heterosexual vs. intravenous drug use, HR 1.75 95%CI 1.12-2.74), lower CD4 cell count at HIV diagnose (comparing with subjects with CD4 ≥ 350/μL at HIV diagnosis, HR for CD4<200/μL was 4.07, and 3.27 for CD4 200~349/μL). Antiretroviral treatment was found a protective factor of KS, with HR 0.39 95%CI 0.27-0.56. Sub-set cohort of Uyghur results were similar.

In part III, we established a hospital-based matched case-control study among HIV-infected Uyghur people and got 39 KS cases and 93 controls. Using conditional logistic regression models, we found HIV transmission route (heterosexual vs. intravenous drug use, Odds Ratio, OR 0.37, 95%CI 0.14-1.00) was risk factor of KS while antiretroviral treatment was protective (OR 0.13, 95%CI 0.03-0.72). Bayesian analysis with priors from Part II and sensitivity analysis found posterior ORs of HIV transmission routes and ART were consistent with national HIV-infected Uyghur cohort.

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