Black Hole as a Wormhole Factory

On general grounds, one may argue that a black hole stops radiation at the Planck mass, where the radiated energy is comparable to the black hole's mass. And also, it has been argued that there would be a "wormhole-like" structure, known as "space-time foam", due to large fluctuations below the Planck length. In this paper, as an explicit example, we consider an exact classical solution which represents nicely those two properties in a recently proposed quantum gravity model based on different scaling dimensions between space and time coordinates. The solution, called "Black Wormhole", consists of two different states, depending on its mass M and an IR parameter omega: For the black hole state, a non-traversable wormhole occupies the interior region of the black hole around the singularity at the origin, whereas for the wormhole state, the interior wormhole is exposed to an outside observer as the black hole horizon is disappeared from evaporation. The black hole state becomes thermodynamically stable as it approaches to the merge point where the interior wormhole throat and the black hole horizon merges, and the Hawking temperature vanishes at the exact merge point. This solution suggests the "Generalized Cosmic Censorship" by the existence of a wormhole-like structure which protects the naked singularity even after the black hole evaporation. One could understand the would-be wormholes inside the black hole horizon as the results of microscopic wormholes created by "negative" energy quanta which have entered the black hole horizon in Hawking radiation processes: The quantum black hole could be a wormhole factory. It is found that this speculative picture may be consistent with the recent "ER=EPR" proposal for resolving the recent black hole entanglement debates.Comment: Added some more words on (1) the transition between the black hole phase and wormhole phase and (2) the notion of a wormhole "factory" in Fig. 5. Updated references, Accepted in PL

Impedance Controlled Twisted String Actuators for Tensegrity Robots

We are developing impedance controlled twisted string actuators (TSA) for use in tensegrity robots, as an alternative to traditional spooled cable actuation. Tensegrity robots are composed of continuous tension and discontinuous compression elements, with no rigid joints between elements, which give them unique force distribution properties. The use of tensegrity robots is strongly motivated by biological examples, and they are capable of locomotion and manipulation by changing lengths of their continuous network of tensional elements, which is also the primary pathways for load transfer through the structure. TSA show the potential to address some of the unique engineering challenges faced by tensegrity structures, and provide unique qualities well suited to an actively controlled tension system, such as compact, light-weight mechanical structures, inherent compliance, variable gearing'', and the ability to transmit high forces with a very low input torque. The inherent variable compliance of impedance control is essential for tensegrity robots to move through and manipulate the environment, and is a natural match to the unique qualities of TSA. This paper briefly introduces the tensegrity robots in the NASA Ames Intelligent Robotics Group and an overview of their future application to space planetary exploration. Then the effectiveness and robustness of TSA are verified through the performance of impedance control modes

Massless Rotating Spacetimes in Four-Dimensional Horava Gravity

We study a particular exact solution for rotating spacetimes in four-dimensional Horava gravity, which has been proposed as a renormalizable gravity model without the ghost problem. We show that the massless Kerr spacetime or the massless Kerr-(A)dS spacetime in Einstein gravity is an exact solution in four-dimensional Horava for an arbitrary IR Lorentz-violation parameter lambda, but with an appropriate cosmological constant. In particular, for the massless topological Kerr-AdS black hole solution with the hyperbolic horizon topology or the massless Kerr-dS cosmological solution with the spherical horizon topology, there exist the ergosphere and the non-vanishing Hawking temperature, which imply the existence of negative mass black holes as well as positive mass spacetimes, by losing its mass from the massless ones via the Hawking radiation or Penrose process in the ergosphere.Comment: 10 pages, 3 figure

A Particle Dispersion Model For Analysis Of Two-Dimensional Mixing In Open Channels

Pollutant mixing in natural rivers is analyzed by using the two-dimensional depth-averaged advection-dispersion model (2D ADE) for rapid completion of the vertical mixing. The dispersion term in the 2D ADE follows Taylor’s assumption (Taylor, 1954; Fischer et al., 1979) which can be applied in the Taylor period. However, most open channel flow has long initial period which makes the skewed concentration distribution due to the unbalance between the shear flow advection and the vertical mixing (Chatwin, 1970). Therefore, the non-Fickian dispersion model is necessary to compensate the limitations of the 2D ADE model. In this research, the two-dimensional particle dispersion model (2D PDM) was developed to analyze the pollutant mixing both in the initial and the Taylor period without determination of the dispersion coefficient. In the 2D PDM, pollutant particles were introduced to visualize physical mixing process according to the complicate flow variation in open channels. The 2D PDM is based on the shear flow dispersion theory and adopted the operator split method which divides the shear advection stage and the turbulent diffusion stage. In the shear advection stage, particles were separated by the vertical velocity deviations in the longitudinal and transverse directions. The separated particles according to the shear flow were mixed across the vertical in the turbulent diffusion stage. After the particle mixing, the particle distribution in each time step was converted to the concentration field for various analysis. The 2D PDM was applied to the straight channel and the meandering channel for analysis of the conservative pollutant mixing. In the straight channel, concentration curves from the 2D PDM showed skewed distribution in the initial period and then turned into the Gaussian distribution in the Taylor period. And, the concentration distributions in the meandering channel showed good agreement with the tracer test results

K-polystability of the first secant varieties of rational normal curves

The first secant variety $\Sigma$ of a rational normal curve of degree $d \geq 3$ is known to be a $\mathbf{Q}$-Fano threefold. In this paper, we prove that $\Sigma$ is K-polystable, and hence, $\Sigma$ admits a weak K\"{a}hler-Einstein metric. We also show that there exists a $(-K_{\Sigma})$-polar cylinder in $\Sigma$.Comment: 17 page

Thermal Design of Astrobee Perching Arm

This paper presents the thermal design of actuators in the perching arm of Astrobee robot that will operate inside the International Space Station (ISS) in starting 2019. Since the crew's safety is of the utmost importance on the ISS, all materials used in the Astrobee robot should meet the touch temperature requirements according to the ISS safety standards to protect crew from skin burns. The Astrobee perching arm consists of 2-DOF arm servo motors and 1-DOF gripper DC motor, which are capable of overheating when stalled, particularly given the lack of gravity-driven thermal convection in the ISS zero-gee environment. Thermal properties of two types of actuators are verified by monitoring the touch temperature in worst-case operations with no thermal protection. Then, the proper thermal protection designs have been conducted and installed to guarantee the safety in all conditions

Primary Tuberculous Abscess of the Spleen in an Immununocompetent Patient Diagnosed by Biochemical Markers and Radiologic Findings

Tuberculous splenic abscess in an immunocompetent patient is extremely rare. We came across a case of middle aged immunocompetent female who presented with abdominal distension, weight loss, and low grade fever. Abdominopelvic computed tomography showed multiple low density lesions in the spleen with ascites. Interferon-gamma release assay was positive and adenosine deaminase level of ascites was significantly high. No primary focus of infection was detected. The patient was diagnosed as having primary multiple tuberculous splenic abscesses with tuberculous peritonitis causing ascites. Follow up computed tomography, after completion of six month course of anti-tubercular therapy, showed splenic abscess and ascites completely disappeared

Myocardial Infarction Thought to be Provoked by Local Epinephrine Injection During Endoscopic Submucosal Dissection

Due to its hemostatic effect, local epinephrine has been used to minimize mucosal bleeding during endoscopic submucosal dissection (ESD), but its clinical benefit remains unclear. On the other hand, several adverse events deemed to be caused by epinephrine have been observed during ESD. A 73-year-old woman developed myocardial infarction after ESD for a large rectal adenoma, and an 80-year-old woman developed abrupt chest tightness during ESD. In both patients, changes on electrocardiogram and elevated cardiac markers provided evidence of myocardial ischemia. The patients were transferred to the cardiac care unit and recovered completely. Up to our knowledge this is the first report of myocardial infarction thought to be provoked by submucosal epinephrine injection during ESD

Thermal Design of Astrobee Perching Arm

This paper presents the thermal design of actuators in the perching arm of Astrobee robot that will operate inside the International Space Station (ISS) starting in 2019. Since the crew's safety is of the utmost importance on the ISS, all materials used in the Astrobee robot should meet the touch temperature requirements according to the ISS safety standards to protect crew from skin burns by controlling the exposure temperature. The Astrobee perching arm consists of 2-DOF (Degrees-of-Freedom)- arm servo motors and 1-DOF gripper DC motor, which are capable of overheating in the stalled condition. Thermal properties of two types of actuators are verified by monitoring the touch temperature in worst-case operations with no thermal protection. Then, the proper thermal protection designs have been conducted and installed to guarantee the safety in all conditions