A low offset dynamic comparator with morphing amplifier

Dynamic comparators are popular structures used in analog circuits such as RFID tags, ADC, memory modules, etc. Compared with traditional open-loop amplifiers that can be used as a comparator, well-designed dynamic comparators are usually faster and more power-efficient, but dynamic CMPs also have some problems. Device mismatch-induced offset voltages is a major challenge when designing dynamic comparators because device mismatch is a random variable that is non-predictable during the design stage. There are many popular dynamic CMP structures; one of them is the Lewis-Gray dynamic comparator [1]. Many authors have introduced alternative dynamic comparator structures which they claim are less affected by device mismatch than the Lewis-Gray circuit but few present a comprehensive and reasonable comparison method. In those papers, different modifications are implemented in order to minimize device mismatch offset, one popular way is to add an amplifier stage before the dynamic comparator. The input signals are amplified in the first amplifier stage before going into the second dynamic comparator stage. Since the outputs of the first stage have a larger difference comparing with the inputs, the offset requirement for the dynamic comparator is loosened. However, the offset still has room for improvement. In this work, a low offset dynamic comparator with morphing amplifier is proposed. It doesn’t have two independent stages. Instead, the amp is inherently integrated into a dynamic comparator, and it yields better offset performance. Moreover, a new fair and comprehensive offset comparison method is also introduced

Is compact urbanity more connected?

The concept of urban compactness is widely accepted as an approach in modern architectural and urban design fields, this belief may vary relative to the density and connectivity of various neighborhoods working within cities of developing countries. Beijing has several compact residential neighborhoods in many of its urban districts. This paper argues that urban compactness as predictor of connectivity may carry an altogether different meaning when compared to the U.S objectives for achieving sustainable compactness by increasing density that is tactically connected. The accelerated pace of migration following the economic progress from the countryside to cities in China helped grew the middle class while shifting demographics has added serious demands of housing and infrastructure within and outside of Beijing districts and its urban core. Various neighborhoods within and round Beijing districts are swelling with unwarranted compactness, causing serious environmental and ecological challenging making basic living conditions unchecked. In addition, crowding, traffic congestion, pollution and limited housing surrounding this compactness is a threat to the public health. Several residential blocks of various sizes in close proximity to each other appear to add physical compactness seemingly well threaded in urban fabric various urban districts. Morphological analysis of selected neighborhoods revealed that many urban neighborhoods similar to case study examples are marred with unregulated urban interventions with little cohesive system of connectivity within these neighborhoods. This study analyzed morphological patterns of street connectivity using Space Syntax method tounderstand if physical compactness also means more connected. The morphological variables notably, integration, connectivity and choice were used as key variables to describe the quality of connectedness of a diverse range of mixed-use commercial and residential typologies that were served by dense street networks. Analysis of spatial morphology of selected compact neighborhoods provided perceptive clues to redevelop a spatial program to bring about a meaningful design intervention to achieve better connections to the unregulated compact urban neighborhoods for achieving more pedestrian-friendly urban neighborhoods that could co-exist with the existing vehicular street networks. The findings indicated that much of mixed-use developments in close proximity to each other were part of a fragmented maze of dead-end streets serving these residential blocks. The incoherent street networks serving these neighborhoods created a lack of control between pedestrian and vehicular circulations causing congestions and unsustainable conditions for social and public realm to coexist

Flares from merged magnetars: their prospects as a new population of gamma-ray counterparts of binary neutron star mergers

Long-lived massive magnetars are expected to be remnants of some binary neutron star (BNS) mergers. In this paper, we argue that the magnetic powered flaring activities of these merged magnetars would occur dominantly in their early millisecond-period-spin phase, which is in the timescale of days. Such flares endure significant absorption by the ejecta from the BNS collision, and their detectable energy range is from 0.1-10 MeV, in a time-lag of $\sim$ days after the merger events indicated by the gravitational wave chirps. We estimate the rate of such flares in different energy ranges, and find that there could have been ~0.1-10 cases detected by Fermi/GBM. A careful search for $\sim10$ milliseconds spin period modulation in weak short gamma-ray bursts (GRBs) may identify them from the archival data. Future MeV detectors can detect them at a rate from a few to tens per year. The recent report on the Quasi-Period-Oscillation found in two BASTE GRBs should not be considered as cases of such flares, for they were detection in a lower energy range and with a much shorter period spin modulation.Comment: 10 pages, 5 figures, submitted to ApJ

Supernovae as gamma ray emitters from the MeV to the TeV

Gamma rays offer unique probes of supernovae as cosmic-ray accelerators and as nucleosynthesis sites. My thesis work focuses on how to explore these two aspects of supernovae. (1) Both starburst galaxies and ultra luminous infrared galaxies are new gamma-ray source classes discovered by Fermi and TeV telescopes. These extreme star-forming galaxies have high supernova rates, and thus accelerating cosmic rays that collide with dense interstellar gas to produce gamma rays. Indeed these galaxies are expected to be "thick" to cosmic-ray protons and thus act as "calorimeters", where a substantial fraction of cosmic-ray energy input is emitted in gamma rays. Here we build a one-zone, "thick-target" model implementing calorimetry and placing a firm upper bound on gamma-ray emission from cosmic-ray interactions. The model assumes that cosmic rays are accelerated by supernovae, and all suffer nuclear interactions rather than escape. Our model has only two free parameters: the cosmic-ray proton acceleration energy per supernova e_cr, and the proton injection spectral index s. We calculate the pionic gamma-ray emission from 10 MeV to 10 TeV, and derive the thick-target parameters for six galaxies with Fermi, H.E.S.S., and/or VERITAS data. Our model provides good fi ts for the M82 and NGC 253, and yields e_cr and s values suggesting that supernova cosmic-ray acceleration is similar in starbursts and in our Galaxy. We find that these starbursts are indeed nearly if not fully proton calorimeters. For NGC 4945 and NGC 1068, the models are consistent with calorimetry but are less well-constrained due to the lack of TeV data. However, the Circinus galaxy and the ultraluminous infrared galaxy Arp 220 exceed our pionic upper-limit; possible explanations are discussed. (2) In our own Galaxy, any supernova explosion would be a spectacular "once in lifetime" event. Tragically, a Galactic Type Ia supernova (SNIa) could go entirely unnoticed due to the large optical and near-IR extinction in the Milky Way plane, low radio and X-ray luminosities, and a weak neutrino signal. But fortunately SNIa emit nuclear gamma-ray lines from 56Ni -> 56Co -> 56Fe radioactive decays. These lines fall within the Fermi/GBM energy range, and the 56Ni 158 keV line is detectable by Swift/BAT. Both instruments frequently monitor the Galactic plane, which is transparent to gamma rays. Thus GBM and BAT are ideal Galactic SNIa early warning systems. We simulate SNIa MeV light curves and spectra to show that GBM and BAT could con rm a Galactic SNIa explosion, followed by Swift localization and observation in X-rays and UVOIR band. The time needed to sound the alarm depends on the 56Ni distribution, and can be as early as a few days if > 10% of the 56Ni is in an exterior shell as suggested by SN2014J gamma data

On the supply of China's healthcare resources in a decentralized healthcare system

The structure of China’s current governance bears prominent features of fiscal decentralization. The supply of healthcare resources in China has clearly witnessed slower growth in the last two decades during which the fiscal decentralization process has taken place. Using China’s provincial panel data, we examine the determinants of healthcare resource supply while paying particular attention to the role of fiscal decentralization. We find that the supply of healthcare resources is inversely related to the degree of decentralization, which, using spatial econometrics, is attributed to the presence of strategic substitutes in healthcare spending across city governments. These findings have important implications for policy makers in making fiscal arrangements among different government tiers

On the supply of China's healthcare resources in a decentralized healthcare system

The structure of China’s current governance bears prominent features of fiscal decentralization. The supply of healthcare resources in China has clearly witnessed slower growth in the last two decades during which the fiscal decentralization process has taken place. Using China’s provincial panel data, we examine the determinants of healthcare resource supply while paying particular attention to the role of fiscal decentralization. We find that the supply of healthcare resources is inversely related to the degree of decentralization, which, using spatial econometrics, is attributed to the presence of strategic substitutes in healthcare spending across city governments. These findings have important implications for policy makers in making fiscal arrangements among different government tiers