Statistics of Extreme Gravitational Lensing Events. I.The Zero Shear Case

For a given source and lens pair, there is a thin on-axis tube-like volume behind the lens in which the radiation flux from the source is greatly increased due to gravitational lensing. Any objects (such as dust grains) which pass through such a thin tube will experience strong bursts of radiation, i.e., Extreme Gravitational Lensing Events (EGLE). We study the physics and statistics of EGLE for the case in which finite source size is more important than shear. One of the several possible significant astrophysical effects is investigated with an illustrative calculation.Comment: revised and final published version including a new section on the destruction of dust grains in globular clusters as an exampl

Genome-inspired molecular identification in organic matter via Raman spectroscopy

Rapid, non-destructive characterization of molecular level chemistry for organic matter (OM) is experimentally challenging. Raman spectroscopy is one of the most widely used techniques for non-destructive chemical characterization, although it currently does not provide detailed identification of molecular components in OM, due to the combination of diffraction-limited spatial resolution and poor applicability of peak-fitting algorithms. Here, we develop a genome-inspired collective molecular structure fingerprinting approach, which utilizes ab initio calculations and data mining techniques to extract molecular level chemistry from the Raman spectra of OM. We illustrate the power of such an approach by identifying representative molecular fingerprints in OM, for which the molecular chemistry is to date inaccessible using non-destructive characterization techniques. Chemical properties such as aromatic cluster size distribution and H/C ratio can now be quantified directly using the identified molecular fingerprints. Our approach will enable non-destructive identification of chemical signatures with their correlation to the preservation of biosignatures in OM, accurate detection and quantification of environmental contamination, as well as objective assessment of OM with respect to their chemical contents

Blow up solutions to a viscoelastic fluid system and a coupled Navier-Stokes/Phase-Field system in R^2

We find explicit solutions to both the Oldroyd-B model with infinite Weissenberg number and the coupled Navier-Stokes/Phase-Field system. The solutions blow up in finite time.Comment: 5 page

Calcium-independent inhibitory G-protein signaling induces persistent presynaptic muting of hippocampal synapses

Adaptive forms of synaptic plasticity that reduce excitatory synaptic transmission in response to prolonged increases in neuronal activity may prevent runaway positive feedback in neuronal circuits. In hippocampal neurons, for example, glutamatergic presynaptic terminals are selectively silenced, creating mute synapses, after periods of increased neuronal activity or sustained depolarization. Previous work suggests that cAMP-dependent and proteasome-dependent mechanisms participate in silencing induction by depolarization, but upstream activators are unknown. We, therefore, tested the role of calcium and G-protein signaling in silencing induction in cultured hippocampal neurons. We found that silencing induction by depolarization was not dependent on rises in intracellular calcium, from either extracellular or intracellular sources. Silencing was, however, pertussis toxin sensitive, which suggests that inhibitory G-proteins are recruited. Surprisingly, blocking four common inhibitory G-protein-coupled receptors (GPCRs) (adenosine A(1) receptors, GABA(B) receptors, metabotropic glutamate receptors, and CB(1) cannabinoid receptors) and one ionotropic receptor with metabotropic properties (kainate receptors) failed to prevent depolarization-induced silencing. Activating a subset of these GPCRs (A(1) and GABA(B)) with agonist application induced silencing, however, which supports the hypothesis that G-protein activation is a critical step in silencing. Overall, our results suggest that depolarization activates silencing through an atypical GPCR or through receptor-independent G-protein activation. GPCR agonist-induced silencing exhibited dependence on the ubiquitin-proteasome system, as was shown previously for depolarization-induced silencing, implicating the degradation of vital synaptic proteins in silencing by GPCR activation. These data suggest that presynaptic muting in hippocampal neurons uses a G-protein-dependent but calcium-independent mechanism to depress presynaptic vesicle release

Study of numerical simulation method modelling gas injection into fractured reservoirs

Purpose. Fractures are the main flow channels in fractured reservoirs. The rapid flow characteristics of gas are outstanding in fractures. It is a major technical problem in the current oilfield development to calculate and accurately describe the fluid flow of this type of reservoir. Methods. This paper improves the calculation model of oil-water-gas phase equilibrium. Based on the discrete fracture net-work model, the numerical simulation mathematical model, numerical model and solution method of nitrogen injection were established. Findings. A simple discrete fracture network model was designed. Numerical simulations verify the correctness of the method. Originality. A fast solution method for gas injection numerical simulation based on discrete crack network model is proposed. Practical implications. The fractured reservoir numerical simulation method can accurately describe the flow of oil, water and gas in the fracture, which lays a foundation for the gas injection development mechanism and gas injection optimization research.Мета. Розробка нової методики чисельного моделювання впорскування газу у тріщинуваті колектори на основі моделі дискретної мережі тріщин. Методика. Для досягнення поставленої мети виконано критичний аналіз відомих методів моделювання, що довів відсутність на сьогоднішній день ефективних методів. Для дослідження проблемних питань у статті застосовано метод розрахунку фазової рівноваги на основі вільної енергії Гіббса як основи для чисельного моделювання закачування газу. Використовували ітераційний метод Ньютона для визначення складу кожної фази в мінімумі вільної енергії Гіббса. Результати. На основі моделі дискретної мережі тріщин сформовані математична модель, чисельна модель і метод рішення для чисельного моделювання закачування газу у тріщинуваті колектори. Правильність методу підтверджується спрощеною моделлю мережі дискретного руйнування. Результати чисельного моделювання узгоджуються з результатами теоретичних розрахунків. Отримана імітаційна модель дискретної мережі тріщин. Встановлено рівняння збереження маси нафти, води, газу та закачаного газу у тріщинах і матриці. Створено рівняння багатофазного потоку рідини у різних середовищах. Наукова новизна. Розроблено новий науково-методичний підхід до розрахунку та чисельного моделювання впорскування газу у тріщинуваті колектори, що враховує дискретну модель мережі тріщин. Практична значимість. Методика чисельного моделювання поведінки тріщинуватого колектору може точно описати потоки нафти, води і газу у тріщині, що сприяє більш детальному вивченню механізму розвитку впорскування газу та його оптимізації.Цель. Разработка новой методики численного моделирования впрыскивания газа в трещиноватые коллекторы на основе модели дискретной сети трещин. Методика. Для достижения поставленной цели выполнен критический анализ известных методов моделирования, доказавший отсутствие на сегодняшний день эффективных методов. Для исследования проблемных вопросов в статье применен метод расчета фазового равновесия на основе свободной энергии Гиббса как основа для численного моделирования закачки газа. Использовали итерационный метод Ньютона для определения состава каждой фазы в минимуме свободной энергии Гиббса. Результаты. На основе модели дискретной сети трещин сформированы математическая модель, численная модель и метод решения для численного моделирования закачки газа в трещиноватые коллекторы. Правильность метода подтверждается упрощенной моделью сети дискретного разрушения. Результаты численного моделирования согласуются с результатами теоретических расчетов. Получена имитационная модель дискретной сети трещин. Установлены уравнения сохранения массы нефти, воды, газа и закачанного газа в трещинах и матрице. Создано уравнение многофазного потока жидкости в различных средах. Научная новизна. Разработан новый научно-методический подход к расчету и численному моделированию впрыскивания газа в трещиноватые коллекторы, учитывающий дискретную модель сети трещин. Практическая значимость. Методика численного моделирования поведения трещиноватого коллектора может точно описать потоки нефти, воды и газа в трещине, что способствует более детальному изучению механизма развития впрыскивания газа и его оптимизации.Project supported by National Science Foundation (No. 51674285), Major National Science and Technology Special Projects (2016ZX05014-004)

Phase transition between non-extremal and extremal Reissner-Nordstr\"om black holes

We discuss the phase transition between non-extremal and extremal Reissner-Nordstr\"om black holes. This transition is considered as the $T \to 0$ limit of the transition between the non-extremal and near-extremal black holes. We show that an evaporating process from non-extremal black hole to extremal one is possible to occur, but its reverse process is not possible to occur because of the presence of the maximum temperature. Furthermore, it is shown that the Hawking-Page phase transition between small and large black holes unlikely occurs in the AdS Reissner-Nordstr\"om black holes.Comment: 12 pages, 6 figures, version to appear in MPL

Not a galaxy: IRAS 04186+5143, a new young stellar cluster in the outer Galaxy

We report the discovery of a new young stellar cluster in the outer Galaxy located at the position of an IRAS PSC source that has been previously mis-identified as an external galaxy. The cluster is seen in our near-infrared imaging towards IRAS 04186+5143 and in archive Spitzer images confirming the young stellar nature of the sources detected. There is also evidence of sub-clustering seen in the spatial distributions of young stars and of gas and dust. Near- and mid-infrared photometry indicates that the stars exhibit colours compatible with reddening by interstellar and circumstellar dust and are likely to be low- and intermediate-mass YSOs with a large proportion of Class I YSOs. Ammonia and CO lines were detected, with the CO emission well centred near the position of the richest part of the cluster. The velocity of the CO and NH$_3$ lines indicates that the gas is Galactic and located at a distance of about 5.5 kpc, in the outer Galaxy. Herschel data of this region characterise the dust environment of this molecular cloud core where the young cluster is embedded. We derive masses, luminosities and temperatures of the molecular clumps where the young stars reside and discuss their evolutionary stages.Comment: 14 pages, 15 figure