Performance Scalability in Communication Networks.

Performance scalability is an essential problem in modern communication networks that expand rapidly. In this dissertation, we consider three models of large-scale communication networks with limited local resources and investigate their asymptotic characteristics as the number of users or the size of the network increases. First, the effectiveness of application-layer coding in a network with a large number of users is considered. The end users encode data packets before transmitting them. The effect of additional packets on the network performance is twofold: (i) additional packets increase offered load, which results in higher drop probability, and (ii) some of dropped packets can be recovered at the receivers after decoding. It is argued that the space of all networks can be partitioned into two regions where coding is beneficial and detrimental, respectively. In particular, we establish an asymptotic regime that contains the boundary between these two regions. On the boundary, networks with and without coding have the same performance. Informally, application-layer coding improves the performance only in networks with low loss probabilities (without coding), and employing such coding in networks with high loss probabilities only degrades the performance. Next, we consider a k-node linear network consisting of bufferless nodes. The asymptotic behavior of the departure process is investigated, as the size of the network increases. Our result provides a complete characterization of a properly scaled limiting departure process, i.e., the joint probability density function of any finite number of consecutive inter-departure times, as the size of the network increases. Finally, linear networks consisting of finite-buffer nodes are considered, and properties of the throughput are investigated, as the size of the network increases. Using an approximation, we establish an asymptotic critical loading regime in which the ratio of the throughput to the input arrival rate is strictly within (0, 1). Such a regime is desirable from the point of view of both the throughput and network cost. Our results indicate that the qualitative behavior of the achievable throughput under the critical regime depends on whether the buffer size is greater than 1.Ph.D.Electrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91568/1/cygene_1.pd

Forbidden Channels and SIMP Dark Matter

In this review, we focus on dark matter production from thermal freeze-out with forbidden channels and SIMP processes. We show that forbidden channels can be dominant to produce dark matter depending on the dark photon and / or dark Higgs mass compared to SIMP.Comment: 5 pages, Prepared for the proceedings of the 13th International Conference on Gravitation, 3-7 July 201

On thermal production of self-interacting dark matter

We consider thermal production mechanisms of self-interacting dark matter in models with gauged $Z_3$ symmetry. A complex scalar dark matter is stabilized by the $Z_3$, that is the remnant of a local dark $U(1)_d$. Light dark matter with large self-interaction can be produced from thermal freeze-out in the presence of SM-annihilation, SIMP and/or forbidden channels. We show that dark photon and/or dark Higgs should be relatively light for unitarity and then assist the thermal freeze-out. We identify the constraints on the parameter space of dark matter self-interaction and mass in cases that one or some of the channels are important in determining the relic density.Comment: 26 pages, 11 figures, Version to appear in Journal of High Energy Physic

Unitary inflaton as decaying dark matter

We consider the inflation model of a singlet scalar field (sigma field) with both quadratic and linear non-minimal couplings where unitarity is ensured up to the Planck scale. We assume that a $Z_2$ symmetry for the sigma field is respected by the scalar potential in Jordan frame but it is broken explicitly by the linear non-minimal coupling due to quantum gravity. We discuss the impacts of the linear non-minimal coupling on various dynamics from inflation to low energy, such as a sizable tensor-to-scalar ratio, a novel reheating process with quartic potential dominance, and suppressed physical parameters in the low energy, etc. In particular, the linear non-minimal coupling leads to the linear couplings of the sigma field to the Standard Model through the trace of the energy-momentum tensor in Einstein frame. Thus, regarding the sigma field as a decaying dark matter, we consider the non-thermal production mechanisms for dark matter from the decays of Higgs and inflaton condensate and show the parameter space that is compatible with the correct relic density and cosmological constraints.Comment: 36 pages, 7 figures, v2: minor corrections made and references added, v3: discussion on preheating added, accepted for Journal of High Energy Physics, v4: Lyman-alpha bound included and inflationary predictions refined for perturbative reheatin

A minimal flavored U(1)′U(1)' for BB-meson anomalies

We consider an anomaly-free $U(1)'$ model with favorable couplings to heavy flavors in the Standard Model(SM), as motivated by $B$-meson anomalies at LHCb. Taking the $U(1)'$ charge to be $Q'=y(L_\mu-L_\tau)+ x(B_3-L_3)$, we can explain the $B$-meson anomalies without invoking extra charged fermions or flavor violation beyond the SM. We show that there is a viable parameter space with a small $x$ that is compatible with other meson decays, tau lepton and neutrino experiments as well as the LHC dimuon searches. We briefly discuss the prospects of discovering the $Z'$ gauge boson at the LHC in the proposed model.Comment: 20 pages, 4 figures, v2: references and discussion on electroweak precision test added, v3: Version to appear in Physical Review

Down-regulation of ROBO2 Expression in Prostate Cancers

Several lines of evidence exist that axon guidance genes are involved in cancer pathogenesis. Axon guidance genes ROBO1 and ROBO2 are candidate tumor suppressor genes (TSG). The aim of our study was to address whether ROBO1 and ROBO2 expressions are altered in prostate cancers (PCA). In this study, we analyzed ROBO1 and ROBO2 expressions in 107 PCAs. In the immunohistochemistry, loss of ROBO2 expression was identified in 66 % of PCAs and was significantly higher than that in normal cells (p < 0.001). By contrast, there was no significant difference of ROBO1 expression between normal and PCAs. Our results indicate that axon guidance protein ROBO2 is frequently lost in PCA and that ROBO2 might be involved in PCA pathogenesis as a candidate TSG

Effects of deep levels on transconductance dispersion in AlGaAs/InGaAs pseudomorphic high electron mobility transistor

The effects of deep levels on the transconductance dispersion in an AlGaAs/InGaAs pseudomorphic high electron mobility transistor was interpreted using capacitance deep level transient spectroscopy (DLTS). Transconductance was decreased by 10% in the frequency range of 10 Hz-10 kHz at the negative gate bias, but it was increased at the positive one. In the DLTS spectra, two hole trap-like signals corresponding to surface states were only observed at the negative pulse bias, whereas the DX-center with the activation energy of 0.42 +/- 0.01 eV were observed at the positive one. The activation energy agrees well with that obtained from the temperature dependence of the positive transconductance dispersion, 0.39 +/- 0.03 eV. These provide evidence that the positive and negative transconductance dispersions are due to the DX center and surface states, respectively.open9