The new social media sites - blogs, micro-blogs, and social networking sites, among others - are gaining considerable momentum to facilitate collaboration and social interactions in general. These sites provide a tremendous asset for understanding social phenomena by providing a wide availability of novel data sources. Recent estimates suggest that social media sites are responsible for as much as one third of new Web content, in the forms of social networks, comments, trackbacks, advertisements, tags, etc. One critical and immediate challenge facing the MIS researchers then becomes - how to effectively utilize this huge wealth of social media data, to facilitate business knowledge discovery and decision making.Among these available data sources, social networks constitute the backbone of almost all social media sites. These network structures provide a rich description of the social scenes and contexts, which is helpful for us to address the above challenge. In this dissertation, I have primarily employed the probabilistic network models, to study various social network related problems arose from the use of social media services. In Chapter 2 and Chapter 3, I studied how information overload can affect the efficiency of information diffusion in online social networks (Delicious.com and Digg.com). Novel diffusion model were proposed to model the observed information overload. The models and their extensions are thoroughly evaluated by solving the Influence Maximization problem related to information diffusion and viral marketing applications. In Chapter 4, I studied the information overload in a micro-blogging application (Twitter.com) using a design science methodology. A content recommendation framework was proposed to help micro-blogging users to efficiently identify quality emergency news feeds. Chapter 5 presents a novel burst detection algorithm concerning identifying and analyzing correlated burst patterns by considering multiple inputs (data streams) that co-evolve over time. The algorithm was later used for discovering burst keywords/tag pairs from online social communities, which are strong indicators of emerging or changing user interests.Chapter 6 concludes this dissertation by highlighting major research contributions and future directions.

This thesis discusses low-power wireline receivers with particular focus on clocking circuitry and architectures. These clocking solutions can be used for a 1-D partial response channel as well as for a conventional DC coupled channel. The receiver front end for a 1-D channel requires more consideration to recover an NRZ signal from the received narrow pulses. Two possible solutions are presented. First, a full-rate detection technique is presented, where the speed is limited by the settling time of a latch circuit which has to be less than 1 UI. Second, a novel demuxing technique is introduced. It is demonstrated through theory, simulation and measurement results that the half-rate architecture can improve maximum achievable speed by a factor of 1.6. The distribution and alignment of high-frequency clocks across a wide bus of links is a signi¯cant challenge in modern computing systems. A low power clock source is demonstrated by incorporating a bu®er into a cross-coupled oscillator. Because the load is isolated from the tank, the oscillator can directly drive 50-Ohm impedances or large capacitive loads with no additional bu®ering. Using this topology, a quadrature VCO (QVCO) is implemented in 0.13 um digital CMOS. The QVCO oscillates at 20 GHz, consumes 20 mW and provides 12% tuning range. Injection locked oscillators (ILOs) are an attractive clocking tool for low-power area- e±cient wireline receivers. In this work, we explored their use as a clock deskew element, a clock recovery unit and a programmable jitter lter. A study of both LC and ring ILOs indicates signi¯cant variation in their jitter tracking bandwidth when used to provide large phase shifts. By selectively injecting di®erent phases of a quadrature-LC or ring VCO, this problem is obviated resulting in reduced phase noise. First, an ILO based half-rate clock recovery technique is presented, which can be used for AC coupled links where low frequency signal components are attenuated by the channel. The nonlinear path comprises a hysteresis latch that recovers the missing low frequency content and a linear path that boosts the high frequency component by taking advantage of the high pass channel response. By optimally combining them, the front-end recovers NRZ signals up to 13 Gb/s burning only 26 mW in 90 nm CMOS. A simple theory and simulation technique for ILO-based receivers is discussed. The clock recovery technique is veried with experimental results at 5-10 Gb/s in 90 nm CMOS consuming 70 mW and acquiring lock within 1.5 ns. Second, a clock forwarded 65nm CMOS receiver uses two ILOs to frequency- multiply, deskew, and track correlated jitter on a pulsed clock forwarded from the transmitter. Di®erent data rates and latency mismatch between the clock and data paths are ac- commodated by a jitter tracking bandwidth that is controllable up to 300MHz. Each receiver consumes 0.92 pJ/bit operating at 7.4 Gb/s and has a jitter tolerance of 1.5 UI at 200MHz.

This thesis discusses low-power wireline receivers with particular focus on clocking circuitry and architectures. These clocking solutions can be used for a 1-D partial response channel as well as for a conventional DC coupled channel. The receiver front end for a 1-D channel requires more consideration to recover an NRZ signal from the received narrow pulses. Two possible solutions are presented. First, a full-rate detection technique is presented, where the speed is limited by the settling time of a latch circuit which has to be less than 1 UI. Second, a novel demuxing technique is introduced. It is demonstrated through theory, simulation and measurement results that the half-rate architecture can improve maximum achievable speed by a factor of 1.6. The distribution and alignment of high-frequency clocks across a wide bus of links is a signi¯cant challenge in modern computing systems. A low power clock source is demonstrated by incorporating a bu®er into a cross-coupled oscillator. Because the load is isolated from the tank, the oscillator can directly drive 50-Ohm impedances or large capacitive loads with no additional bu®ering. Using this topology, a quadrature VCO (QVCO) is implemented in 0.13 um digital CMOS. The QVCO oscillates at 20 GHz, consumes 20 mW and provides 12% tuning range. Injection locked oscillators (ILOs) are an attractive clocking tool for low-power area- e±cient wireline receivers. In this work, we explored their use as a clock deskew element, a clock recovery unit and a programmable jitter lter. A study of both LC and ring ILOs indicates signi¯cant variation in their jitter tracking bandwidth when used to provide large phase shifts. By selectively injecting di®erent phases of a quadrature-LC or ring VCO, this problem is obviated resulting in reduced phase noise. First, an ILO based half-rate clock recovery technique is presented, which can be used for AC coupled links where low frequency signal components are attenuated by the channel. The nonlinear path comprises a hysteresis latch that recovers the missing low frequency content and a linear path that boosts the high frequency component by taking advantage of the high pass channel response. By optimally combining them, the front-end recovers NRZ signals up to 13 Gb/s burning only 26 mW in 90 nm CMOS. A simple theory and simulation technique for ILO-based receivers is discussed. The clock recovery technique is veried with experimental results at 5-10 Gb/s in 90 nm CMOS consuming 70 mW and acquiring lock within 1.5 ns. Second, a clock forwarded 65nm CMOS receiver uses two ILOs to frequency- multiply, deskew, and track correlated jitter on a pulsed clock forwarded from the transmitter. Di®erent data rates and latency mismatch between the clock and data paths are ac- commodated by a jitter tracking bandwidth that is controllable up to 300MHz. Each receiver consumes 0.92 pJ/bit operating at 7.4 Gb/s and has a jitter tolerance of 1.5 UI at 200MHz.

Type I X-ray bursts (XRB) are highly energetic and explosive astrophysical events, observed as very sudden and intense emissions of X-rays. X-ray bursts are believed to be powered by a thermonuclear runaway on the surface of a neutron star in a binary system. XRB models are dependent on the accurate information of the nuclear reactions involved. The 18Ne(α,p)21Na reaction is considered to be of great importance as a possible breakout route from the Hot-CNO cycle preceding the thermonuclear runaway. In this thesis work, the 18Ne(α,p)21Na reaction cross-section was indirectly measured at Ecm(α,p) = 2568, 1970, 1758, 1683, 1379 and 1194 keV, using the time-reverse 21Na(p,α)18Ne reaction. Since the time-reverse approach only connects the ground states of 21Na and 18Ne, the cross sections measured here represent lower limits of the 18Ne(α,p)21Na cross-section. An experiment was performed using the the ISAC-II facility at TRIUMF, Vancouver, Canada. A beam of 21Na ions was delivered to a polyethylene (CH2)n target placed within the TUDA scattering chamber. The reaction 18Ne and 4He ions were detected using silicon strip detectors, with time-of-flight and ΔE/E particle identification techniques used to distinguish the ions from background. The measurement at Ecm = 1194 keV is the lowest energy measurement to date of the 18Ne(α,p)21Na cross section. The measured cross sections presented in this thesis were compared to the NON-SMOKER Hauser-Feshbach statistical calculations of the cross section and to the unpublished results of another time-reverse investigation performed by a collaboration at the Argonne National Laboratory. A 18Ne(α,p)21Na reaction rate calculation based on the measured cross sections was performed. In comparison with previous reaction rate estimates, our results indicate a rate that is about a factor 2-3 lower than Hauser-Feshbach calculations, suggesting that a statistical approach may not be appropriate for cross section calculations for nuclei in this mass region. The astrophysical consequences of our new results appear to remain nevertheless negligible. These are also presented in this thesis.

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / How to rise the reliability of the data transmission is one of the main problem faced by modern digital communication designers. This paper studies the error-correcting codes being suitable for the channel existing both the random and burst error. A new error control scheme is given. The scheme is a concatenated coding system using an interleaved Reed-Solomon code with symbols over GF (24) as the outer code and a Viterbi-decoded convolutional code as the inner code. As a result of the computer simulation, it is proved that the concatenated coding system has a output at a very low bit error rate (BER)and can correct a lot of compound error patterns. It is suitable for the serious disturb channel existing both the random and burst error. This scheme will be adopted for a remote control system.

The merger of a neutron star (NS) binary may result in the formation of a rapidly spinning magnetar. The magnetar can potentially survive for seconds or longer as a supramassive NS before collapsing to a black hole if, indeed, it collapses at all. During this process, a fraction of the magnetar's rotational energy of similar to 10(53) erg is transferred via magnetic spin-down to the surrounding ejecta. The resulting interaction between the ejecta and the surrounding circumburst medium powers a year-long or greater synchrotron radio transient. We present a search for radio emission with the Very Large Array following nine short-duration gamma-ray bursts (GRBs) at rest-frame times of approximate to 1.3-7.6 yr after the bursts, focusing on those events that exhibit early-time excess X-ray emission that may signify the presence of magnetars. We place upper limits of less than or similar to 18-32 mu Jy on the 6.0 GHz radio emission, corresponding to spectral luminosities of less than or similar to(0.05-8.3) x 10(39) erg s(-1). Comparing these limits to the predicted radio emission from a long-lived remnant and incorporating measurements of the circumburst densities from broadband modeling of short GRB afterglows, we rule out a stable magnetar with an energy of 10(53) erg for half of the events in our sample. A supramassive remnant that injects a lower rotational energy of 10(52) erg is ruled out for a single event, GRB 050724A. This study represents the deepest and most extensive search for long-term radio emission following short GRBs to date, and thus the most stringent limits placed on the physical properties of magnetars associated with short GRBs from radio observations.

The 5-year survival rate for ovarian cancer is only 45% largely due to lack of effective screening methods. Current methods include palpation, transvaginal ultrasound, and the CA-125 blood test. Finding disease reliably and at an early stage increase survival to 92%. We have designed and built a 0.7 mm endoscope for the early detection of ovarian cancer. Inserted transvaginally through the working channel of a hysteroscope, the falloposcope creates a minimally invasive procedure for the screening of high risk women. To improve the ease-of-use and safety of falloposcope deployment, we are working to create an everting balloon. Currently, the falloposcope would require a skilled user to operate due to the challenging anatomy of the fallopian tubes - a small opening from the uterus (< 1 mm), tortuous path, and delicate lumenal features. A balloon delivery system would gently open the fallopian tube and guide the falloposcope down the center of lumen. We show balloon design and discuss integration with the falloposcope prototype. We test possible mechanical damage to the tissue due to scraping, puncture, or overstretching. Successful introduction of the everting balloon to simplify falloposcope delivery could expand screening beyond specialized centers to smaller clinical locations.

A computational model of a midbrain dopamine neuron was extended in this study to include a response to random excitatory afferent input by incorporating the receptor components AMPA and NMDA. In a diagonal band where average glutamatergic and tonic gabaergic input is roughly balanced, both single spike firing and bursting can be observed. Simulated SK channel block strengthens the correlation between pattern and rate and increases the number of spikes fired in bursts by increasing the spikes per burst. A simulated doubling of the AMPA/NMDA ratio leads to a frequency increase that becomes more prominent at high firing rates, and an increase in the percent spikes fired in bursts. Changes in pattern and rate are poorly correlated in the model. Manipulations of the neuron greatly depend on the background level of synaptic inputs, suggesting that interpretation of population data from dopamine neurons requires taking variability into account rather than averages.

No description available.

In dieser Arbeit untersuchen wir die Produktion von Neutrinos in astrophysikalischen Quellen. Bei der Beschreibung der Wechselwirkung betrachten wir resonante, direkte und Multipion-Produktion. Zusätzlich berücksichtigen wir die Produktion von Neutronen und positiv geladenen Kaonen. Wir beachten explizit die Energieverluste der Sekundärteilchen - Pionen, Myonen und Kaonen - auf Grund von Synchrotronstrahlung derselben und adiabatischer Expansion. In Bezug auf den Neutrinofluss berücksichtigen wir Flavor-Mischungen der Neutrinos auf dem Weg zum Beobachter. Zunächst führen wir eine Analyse basierend auf einem generischen Quellmodell durch, in der wir den Einfluss von Magnetfeld und Größe der Quelle auf die Neutrinospektren und das Verhältnis der verschiedenen Neutrino-Flavor untersuchen. Es stellt sich heraus, dass man im Rahmen dieses generischen Modells verschiedene Regionen im Parameterraum anhand des Flavor-Verhältnisses, das für hohe Magnetfelder von dem zumeist angenommenen Verhältnis (nu_e:nu_mu:nu_tau)=(1:2:0) abweicht, klassifizieren kann. In einer zweiten Analyse bestimmen wir die erwarteten Neutrinospektren von Gammablitzen im Rahmen des Feuerball-Modells aus beobachteten Photonspektren. Es zeigt sich, dass auf Grund grober Abschätzungen in der Literatur, der Neutrinofluss zumeist um etwa eine Größenordnung überschätzt wird. Deshalb berechnen wir den erwarteten Neutrinofluss der Gammablitze neu, die während der 40-Leinen-Konfiguration des IceCube-Detektors gemessen wurden, und folgern, dass entgegen der Behauptung der IceCube-Kollaboration, das Feuerball-Modell noch nicht ausgeschlossen ist. Des Weiteren quantifizieren wir systematische und astrophysikalische Unsicherheiten in dem vorhergesagten Neutrinofluss. / In this work we investigate the photohadronic neutrino production within astrophysical environments. In the description of the photohadronic interactions we consider resonant, direct and multipion production. In addition we include the production of neutrons and positiv charged kaons. For the secondaries - pions, muons, kaons - we take into account the effects of energy losses due to synchrotron radiation and adiabatic expansion. We also consider flavor effects on the neutrino flux. In a first analysis we define a generic model for a neutrino source and investigate the effect of the magnetic field and the size of the source on the neutrino flux and flavor ratio. We find that within the model we can classify different regions in the parameter space by the flavor ratio which for higher magnetic field differs from the often used assumption of (nu_e:nu_mu:nu_tau)=(1:2:0). In a second analysis we recompute the expected neutrino flux expected from gamma-ray bursts in the fireball model and see that the neutrino flux in the literature typically overestimates the flux by one order of magnitude due to rough approximations. We therefore reconsider the expected neutrino flux from the gamma-ray bursts measured during the 40-string-configuration of IceCube. As a result we conclude that against the claim of the IceCube collaboration the fireball model is not excluded yet. Furthermore we quantify the systematical and astrophysical uncertainties on the neutrino flux prediction.