Stochastic gravitational-wave background from spin loss of black holes

Although spinning black holes are shown to be stable in vacuum in general relativity, there exists exotic mechanisms that can convert the spin energy of black holes into gravitational waves. Such waves may be very weak in amplitude, since the spin-down could take a long time, and a direct search may not be feasible. We propose to search for the stochastic background associated with the spin-down, and we relate the level of this background to the formation rate of spinning black holes from the merger of binary black holes, as well as the energy spectrum of waves emitted by the spin-down process. We argue that current LIGO-Virgo observations are not inconsistent with the existence of a spin-down process, as long as it is slow enough. On the other hand, the background may still exist as long as a moderate fraction of spin energy is emitted within Hubble time. This stochastic background could be one interesting target of next generation GW detector network, such as LIGO Voyager, and could be extracted from total stochastic background

Geometric Inference on Kernel Density Estimates

We show that geometric inference of a point cloud can be calculated by examining its kernel density estimate with a Gaussian kernel. This allows one to consider kernel density estimates, which are robust to spatial noise, subsampling, and approximate computation in comparison to raw point sets. This is achieved by examining the sublevel sets of the kernel distance, which isomorphically map to superlevel sets of the kernel density estimate. We prove new properties about the kernel distance, demonstrating stability results and allowing it to inherit reconstruction results from recent advances in distance-based topological reconstruction. Moreover, we provide an algorithm to estimate its topology using weighted Vietoris-Rips complexes.Comment: To appear in SoCG 2015. 36 pages, 5 figure

CdTe Quantum Dot Fluorescence Thermometry of Rolling Bearing

Temperature is one of the most important parameters affecting the service life and performance of a rolling element bearing component. In this paper, a nonintrusive method is developed to monitor the temperature variation of the inner raceway during bearing operation utilizing CdTe quantum dots as the temperature sensors. The CdTe quantum dots were synthesized and were used in constructing a sensor film by means of layer-by-layer electrostatic self-assembly method on an ultrathin glass slice. The peak wavelength shift of the fluorescence spectrum of the sensor film shows a linear and reversible relationship with temperature, and it is used to sense the temperature of the inner raceway. The resolution of the CdTe optothermal sensor is determined to be 0.14 nm/°C. The temperature measurement of rolling element bearing was conducted on a bearing test rig incorporated with an optical fiber fluorescence spectrum detecting system. To verify the accuracy of the temperature obtained by quantum dots sensor film, a thermocouple was used to test the temperature of the inner raceway right before and after the operation. Results show that the temperature obtained by the CdTe quantum dots film sensor is consistent with that by the thermocouple, with an error typically below 10% or smaller

Adsorption of Antibiotics and Nickel from Aqueous Solutions on Heterogeneous Adsorbents Based on Barley Straw

Water security is essential in order to achieve sustainability. Concerns of antibiotic-contaminated water bodies have prompted research of effective water treatment technologies. Researchers are particularly concerned about two commonly prescribed fluoroquinolones antibiotics with broad-spectrum activity and good oral absorption: levofloxacin (LEV) and norfloxacin (NOR). However, these drugs cannot be completely metabolized in humans or animals, nor can they be effectively removed using current wastewater treatment technologies such as activated sludge. As a result, they are discharged into the environment and become emerging environmental contaminants, which coexist with metals such as nickel ions in diverse aquatic systems. Consequently, they may threaten human health. Adsorption, the partitioning of a target compound between the fluid and adsorbent phase, is an alternative technology for pollutant removal. In this work, raw barley straw (RBS)--an abundantly generated agricultural byproduct mainly composed of cellulose, hemicellulose, and lignin--was pretreated by H3PO4 impregnation and microwave heating. This pretreated barley straw (PBS) was used as an adsorbent for the removal of LEV, NOR, and nickel ions, which are representatives of antibiotics and heavy metals, from artificial wastewater. The research included the following phases: 1. Phase I: Pretreatment and characterization of adsorbents based on barley straw. PBS that had a high surface area (1314 ± 10 m2/g) was obtained at conditions of 5% (w/v) H3PO4 impregnation concentration and 9 min 700 W microwave heating. The total organic carbon (TOC) released into suspensions from the adsorbents significantly reduced from 34.4 ± 0.9 mg/g (RBS) to 0.9 ± 0.2 mg/g (PBS) indicating the enhanced stability of PBS. Barley straw adsorbents were characterized by particle size distribution, elemental compositions, scanning electron microscopy, and thermogravimetric analysis. 2. Phase II: Adsorption of LEV on PBS. PBS demonstrated high LEV adsorption capacities in a wide range of solution pH (2.47-9.60). The experimental maximum LEV adsorption capacity of PBS (408 ± 5 mg LEV/g at pH 6.88 and 298.15 K) was much higher than that of RBS and the reported adsorbents. The adsorption kinetics and equilibrium at different temperatures were investigated, and the kinetic and isotherm data were well-fitted by the pseudo-second-order kinetic model and Langmuir-Freundlich model, revealing that the adsorption of LEV on PBS was an endothermic process. The activation energy was determined to be 45.9 kJ/mol. The desorption of LEV loaded on PBS was examined, and the site energy and its distribution of PBS for LEV adsorption were estimated. The weighted mean and standard deviation of the distribution were employed to depict the interaction strength between the adsorbent and adsorbate, and adsorption heterogeneity. The π-π electron-donor-acceptor (EDA) interaction between the π* aromatic C=C of PBS and the π* carbon atom in the benzene ring attached to fluorine of LEV was proposed as one of the major adsorption mechanisms. Such interaction was investigated by C K-edge X-ray absorption near-edge structure (XANES) spectroscopy. 3. Phase III: Adsorption of NOR on PBS. High NOR adsorption capacities of PBS were also obtained in a wide pH range (2.67-10.50). The experimental maximum NOR adsorption capacity of PBS (396 ± 14 mg NOR/g at pH 6.96 and 298.15 K) was much higher than that of RBS and the reported adsorbents. The adsorption kinetics and equilibrium with respect to temperature were evaluated using the pseudo-second-order kinetic model and Langmuir-Freundlich model, respectively. The adsorption of NOR on PBS was an endothermic processes with an activation energy of 22.2 kJ/mol. The desorption of NOR loaded on PBS was also examined. The adsorption site energy and its distribution were also determined to exhibit the adsorption mechanism. At the tested temperatures of 298.15-318.15 K, the higher the temperature, the higher the weighted mean (therefore the stronger the adsorption affinity), and the slightly weaker the heterogeneity. The percentage of adsorption sites, whose site energy is greater than or equal to a specific E* value, was estimated. The proposed dominant forces, EDA interactions (n-π and π-π), were investigated by the C and O K-edge XANES spectroscopy. 4. Phase IV: Adsorption of nickel on PBS and impact of nickel on LEV adsorption. The adsorption isotherms of nickel on PBS and RBS were well-fitted using the Langmuir-Freundlich model. Solution pH played an important role during the nickel adsorption process. Results of XANES and extended X-ray absorption fine structure spectroscopy indicated that the adsorbed Ni remained the same oxidation state (II) as NiSO4 and was associated with 6 oxygen atoms from water or the functional groups of PBS (e.g., carboxyl group) at an atomic distance of 2.043 ± 0.013 Å. The site energy and its distributions of PBS and RBS for nickel adsorption were determined and demonstrated that the adsorption affinity between PBS and nickel was stronger than that of RBS. Ni(II) slightly suppressed the LEV adsorption on PBS at the tested pH values (4.0, 7.0, and 9.0) since the cationic Ni(II) competed with LEV for the negatively charged adsorption sites of PBS. 5. Phase V: The extended application of PBS in selective water removal from water-ethanol mixture was investigated to produce fuel grade ethanol. PBS demonstrated a higher water adsorption capacity (0.63 ± 0.02 mol/g) and a close water to ethanol adsorption ratio (4.85) compared with RBS (0.50 ± 0.01 mol/g and 5.00). Utilization of PBS in ethanol concentration can be optimized by a dynamic system control in order to achieve a higher concentration of ethanol

Chatbot Catalysts: Improving Team Decision-Making Through Cognitive Diversity and Information Elaboration

As the integration of artificial intelligence (AI) into team decision-making continues to expand, it is both theoretically and practically pressing for researchers to understand the impact of the technology on team dynamics and performance. To investigate this relationship, we conducted an online experiment in which teams made decisions supported by chatbots and employed computational methods to analyze team interaction processes. Our results indicated that compared to those assisted by chatbots in later phases, teams receiving chatbot assistance during the initial phase of their decision-making process exhibited increased cognitive diversity (i.e., diversity in shared information) and information elaboration (i.e., exchange and integration of information). Ultimately, teams assisted by chatbots early on performed better. These results imply that introducing AI at the beginning of the process can enhance team decision-making by promoting effective information sharing among team members

It Depends on the Timing: The Ripple Effect of AI on Team Decision-Making

Whereas artificial intelligence (AI) is increasingly used to facilitate team decision-making, little is known about how the timing of AI assistance may impact team performance. The study investigates this question with an online experiment in which teams completed a new product development task with assistance from a chatbot. Information needed for making the decision was distributed among the team members. The chatbot shared information critical to the decision in either the first half or second half of team interaction. The results suggest that teams assisted by the chatbot in the first half of the decision-making task made better decisions than those assisted by the chatbot in the second half. Analysis of team member perceptions and interaction processes suggests that having a chatbot at the beginning of team interaction may have generated a ripple effect in the team that promoted information sharing among team members

High-Q exterior whispering gallery modes in a metal-coated microresonator

We propose a kind of plasmonic whispering gallery modes highly localized on the exterior surface of a metal-coated microresonator. This exterior (EX) surface mode possesses high quality factors at room temperature, and can be efficiently excited by a tapered fiber. The EX mode can couple to an interior (IN) mode and this coupling produces a strong anti-crossing behavior, which not only allows conversion of IN to EX modes, but also forms a long-lived anti-symmetric mode. As a potential application, the EX mode could be used for a biosensor with a sensitivity high up to 500 nm per refraction index unit, a large figure of merit, and a wide detection range

Cavity QED treatment of scattering-induced efficient free-space excitation and collection in high-Q whispering-gallery microcavities

Whispering-gallery microcavity laser possesses ultralow threshold, whereas convenient free-space optical excitation and collection suffer from low efficiencies due to its rotational symmetry. Here we analytically study a three-dimensional microsphere coupled to a nano-sized scatterer in the framework of quantum optics. It is found that the scatterer is capable of coupling light in and out of the whispering-gallery modes (WGMs) without seriously degrading their high-Q properties, while the microsphere itself plays the role of a lens to focus the input beam on the scatterer and vice versa. Our analytical results show that (1) the high-Q WGMs can be excited in free space, and (2) over 50% of the microcavity laser emission can be collected within less than ${1}^{\circ}$. This coupling system holds great potential for low threshold microlasers free of external couplers.Comment: 10 pages, 8 figure

Strongly enhanced light-matter interaction in a hybrid photonic-plasmonic resonator

We propose a hybrid photonic-plasmonic resonant structure which consists of a metal nanoparticle (MNP) and a whispering gallery mode (WGM) microcavity. It is found that the hybrid mode enables a strong interaction between the light and matter, and the single-atom cooperativity is enhanced by more than two orders of magnitude compared to that in a bare WGM microcavity. This remarkable improvement originates from two aspects: (1) the MNP offers a highly enhanced local field in the vicinity of an emitter, and (2), surprisingly, the high-\textit{Q} property of WGMs can be maintained in the presence of the MNP. Thus the present system has great advantages over a single microcavity or a single MNP, and holds great potential in quantum optics, nonlinear optics and highly sensitive biosening.Comment: 5 pages, 4 figure