Star formation and molecular hydrogen in dwarf galaxies: a non-equilibrium view

We study the connection of star formation to atomic (HI) and molecular hydrogen (H$_2$) in isolated, low metallicity dwarf galaxies with high-resolution ($m_{\rm gas}$ = 4 M$_\odot$, $N_{\rm ngb}$ = 100) SPH simulations. The model includes self-gravity, non-equilibrium cooling, shielding from an interstellar radiation field, the chemistry of H$_2$ formation, H$_2$-independent star formation, supernova feedback and metal enrichment. We find that the H$_2$ mass fraction is sensitive to the adopted dust-to-gas ratio and the strength of the interstellar radiation field, while the star formation rate is not. Star formation is regulated by stellar feedback, keeping the gas out of thermal equilibrium for densities $n <$ 1 cm$^{-3}$. Because of the long chemical timescales, the H$_2$ mass remains out of chemical equilibrium throughout the simulation. Star formation is well-correlated with cold ( T $\leqslant$ 100 K ) gas, but this dense and cold gas - the reservoir for star formation - is dominated by HI, not H$_2$. In addition, a significant fraction of H$_2$ resides in a diffuse, warm phase, which is not star-forming. The ISM is dominated by warm gas (100 K $<$ T $\leqslant 3\times 10^4$ K) both in mass and in volume. The scale height of the gaseous disc increases with radius while the cold gas is always confined to a thin layer in the mid-plane. The cold gas fraction is regulated by feedback at small radii and by the assumed radiation field at large radii. The decreasing cold gas fractions result in a rapid increase in depletion time (up to 100 Gyrs) for total gas surface densities $\Sigma_{\rm HI+H_2} \lesssim$ 10 M$_\odot$pc$^{-2}$, in agreement with observations of dwarf galaxies in the Kennicutt-Schmidt plane.Comment: Accepted for publication in MNRAS. Changes (including a pamameter study in Appendix C) highlighte

How Important Are Risk-Taking Incentives in Executive Compensation?

This paper investigates whether observed executive compensation contracts are designed to provide risk-taking incentives in addition to effort incentives. We develop a stylized principal-agent model that captures the interdependence between firm risk and managerial incentives. We calibrate the model to individual CEO data and show that it can explain observed compensation practice surprisingly well. In particular, it justifies large option holdings and high base salaries. Our analysis suggests that options should be issued in the money. If tax effects are taken into account, the model is consistent with the almost uniform use of at-the-money stock options. We conclude that the provision of risk-taking incentives is a major objective in executive compensation practice

Thermally-Switchable Metalenses Based on Quasi-Bound States in the Continuum

Dynamic wavefront shaping with optical metasurfaces has presented a major challenge and inspired a large number of highly elaborate solutions. Here, we experimentally demonstrate thermo-optically reconfigurable, nonlocal metasurfaces using simple device architectures and conventional CMOS-compatible dielectric materials. These metasurfaces support quasi-bound states in the continuum (q-BICs) derived from symmetry breaking and encoded with a spatially varying geometric phase, such that they shape optical wavefront exclusively on spectrally narrowband resonances. Due to the enhanced light-matter interaction enabled by the resonant q-BICs, a slight variation of the refractive index introduced by heating and cooling the entire device leads to a substantial shift of the resonant wavelength and a subsequent change to the optical wavefront associated with the resonance. We experimentally demonstrate a metalens modulator, the focusing capability of which can be thermally turned on and off, and reconfigurable metalenses, which can be thermo-optically switched to produce two distinct focal patterns. Our devices offer a pathway to realize reconfigurable, multifunctional meta-optics using established manufacturing processes and widely available dielectric materials that are conventionally not considered "active" materials due to their small thermo-optic or electro-optic coefficients

Energy Efficiency Modeling and Analysis in Wireless Sensor Networks

We propose here an extended linear feedback model, taking the binary exponential backo® mechanism adopted in IEEE 802.15.4 CSMA/CA and analyse the energy consumption issues of the one hop sensor nodes. Numerical results show that the energy consumption in Wireless Sensor Networks (WSNs) can be reduced by applying CSMA protocol with ¯xed contention window size. Besides, an optimal contention window size can achieve the reasonable successful probability of the packet transmission without extra wastage of the battery power

Cosmic Sands II: Challenges in Predicting and Measuring High-z Dust Temperatures

In the current era of high-z galaxy discovery with JWST and ALMA, our ability to study the stellar populations and ISM conditions in a diverse range of galaxies at Cosmic Dawn has rapidly improved. At the same time, the need to understand the current limitations in modeling galaxy formation processes and physical properties in order to interpret these observations is critical. Here, we study the challenges in modeling galaxy dust temperatures, both in the context of forward modeling galaxy spectral properties from a hydrodynamical simulation and via backwards modeling galaxy physical properties from mock observations of far-infrared dust emission. We find that, especially for the most massive objects in our sample, neglecting to account for far-infrared dust optical depth can significantly bias the dust properties derived from SED modeling. Anisotropies in infrared emission, driven by the clumpy nature of early star and structure formation, leads to an orientation angle bias in quantities like infrared luminosities and apparent dust temperatures measured from galaxy SEDs. We caution that conclusions inferred from both hydrodynamical simulations and observations alike are susceptible to unique and nuanced uncertainties that can limit the usefulness of current high-z dust measurements.Comment: 17 pages, 12 figures. Submitted to ApJ. Comments welcome

Ontology-Based Privacy Protection in Location Commerce

Location commerce extends e-commerce through the provision of location-related activities, but this gives rise to greater concerns about privacy invasion. To encourage the smooth growth of location commerce, it is suggested that control over the sharing of intimate information be given back to the consumer. This study proposes an ontology-based privacy protection (OPP) framework that allows consumers to specify their own privacy preferences and then uses these preferences to determine whether or not a message from a merchant can be delivered to a consumer. We use ontology to structure the knowledge to simplify the framework and allow for the possibility of automation. The system is believed to be context-aware, as the location, time, service type, information type, and other contextual data are taken into consideration. We develop a prototype system for demonstration and experiment, and show that the framework design is feasible and has a reasonable performance

A Statistical Analysis of Industrial Penetration and Internet Intensity in Taiwan

This paper investigates the effect of industrial penetration (geographic concentration of industries) and internet intensity (the proportion of enterprises that use the internet) for Taiwan manufacturing firms, and analyses whether the relationships are substitutes or complements. The sample observations are based on 153,081 manufacturing plants, and covers 26 two-digit industry categories and 358 geographical townships in Taiwan. The Heckman selection model is used to accommodate sample selectivity for unobservable data for firms that use the internet. The empirical results from two-stage estimation show that: (1) a higher degree of industrial penetration will not affect the probability that firms will use the internet, but will affect the total expenditure on internet intensity; (2) for two-digit SIC industries, industrial penetration generally decreases the total expenditure on internet intensity; and (3) industrial penetration and internet intensity are substitutes

Industrial Penetration and Internet Intensity

This paper investigates the effect of industrial penetration and internet intensity for Taiwan manufacturing firms, and analyses whether the relationships are substitutes or complements. The sample observations are based on 153,081 manufacturing plants, and covers 26 two-digit industry categories and 358 geographical townships in Taiwan. The Heckman selection model is used to accommodate sample selectivity for unobservable data for firms that use the internet. The empirical results from two-stage estimation show that: (1) a higher degree of industrial penetration will not affect the probability that firms will use the internet, but will affect the total expenditure on internet intensity; (2) for two-digit industries, industrial penetration generally decreases the total expenditure on internet intensity; and (3) industrial penetration and internet intensity are substitutes

Essays of Executive Compensation - Managerial Incentives and Disincentives

Executive compensation has been a central point of debates for the past 20 years, both in the academic circle and in Wall Street Journal. Have shareholders paid too much to the CEOs, or are the pay packages necessary for recruiting and keeping managerial talents? Are the structures of the pay packages reasonable, or are the compensation packages designed the way they are simply to facilitate more manipulation? The end to the debate between perspectives of "rent-seeking" (i.e., executives are always stealing shareholdersmoney away) ands "efficient contracting" (i.e., executive pays are set with economic rationales by their shareholders) does not appear to be coming any time soon. The thesis contributes to this debate by rst identifying rms whose CEOs are more optimisitic about their rmsprospects are more likely to experience crashes in stock prices. Subsquently in Chapter 3 and 4, the thesis aims to o¤er economic explanations for current compensation structures