Cosmological Multi-Black Hole Solutions

We present simple, analytic solutions to the Einstein-Maxwell equation, which describe an arbitrary number of charged black holes in a spacetime with positive cosmological constant $\Lambda$. In the limit $\Lambda=0$, these solutions reduce to the well known Majumdar-Papapetrou (MP) solutions. Like the MP solutions, each black hole in a $\Lambda >0$ solution has charge $Q$ equal to its mass $M$, up to a possible overall sign. Unlike the $\Lambda = 0$ limit, however, solutions with $\Lambda >0$ are highly dynamical. The black holes move with respect to one another, following natural trajectories in the background deSitter spacetime. Black holes moving apart eventually go out of causal contact. Black holes on approaching trajectories ultimately merge. To our knowledge, these solutions give the first analytic description of coalescing black holes. Likewise, the thermodynamics of the $\Lambda >0$ solutions is quite interesting. Taken individually, a $|Q|=M$ black hole is in thermal equilibrium with the background deSitter Hawking radiation. With more than one black hole, because the solutions are not static, no global equilibrium temperature can be defined. In appropriate limits, however, when the black holes are either close together or far apart, approximate equilibrium states are established.Comment: 15 pages (phyzzx), UMHEP-380 (minor referencing error corrected

Pair Creation of Dilaton Black Holes

We consider dilaton gravity theories in four spacetime dimensions parametrised by a constant $a$, which controls the dilaton coupling, and construct new exact solutions. We first generalise the C-metric of Einstein-Maxwell theory ($a=0$) to solutions corresponding to oppositely charged dilaton black holes undergoing uniform acceleration for general $a$. We next develop a solution generating technique which allows us to ``embed" the dilaton C-metrics in magnetic dilaton Melvin backgrounds, thus generalising the Ernst metric of Einstein-Maxwell theory. By adjusting the parameters appropriately, it is possible to eliminate the nodal singularities of the dilaton C-metrics. For $a<1$ (but not for $a\ge 1$), it is possible to further restrict the parameters so that the dilaton Ernst solutions have a smooth euclidean section with topology $S^2\times S^2-{\rm\{pt\}}$, corresponding to instantons describing the pair production of dilaton black holes in a magnetic field. A different restriction on the parameters leads to smooth instantons for all values of $a$ with topology $S^2\times \R^2$.Comment: 22 pages, EFI-93-51, FERMILAB-Pub-93/272-A, UMHEP-393. (Asymptotics of Ernst solutions clarified, typos repaired

Universal corrections to entanglement entropy of local quantum quenches

We study the time evolution of single interval Renyi and entanglement entropies following local quantum quenches in two dimensional conformal field theories at finite temperature for which the locally excited states have a finite temporal width, \epsilon. We show that, for local quenches produced by the action of a conformal primary field, the time dependence of Renyi and entanglement entropies at order \epsilon^2 is universal. It is determined by the expectation value of the stress tensor in the replica geometry and proportional to the conformal dimension of the primary field generating the local excitation. We also show that in CFTs with a gravity dual, the \epsilon^2 correction to the holographic entanglement entropy following a local quench precisely agrees with the CFT prediction. We then consider CFTs admitting a higher spin symmetry and turn on a higher spin chemical potential \mu. We calculate the time dependence of the order \epsilon^2 correction to the entanglement entropy for small \mu, and show that the contribution at order \mu^2 is universal. We verify our arguments against exact results for minimal models and the free fermion theory

STUDI EKSPERIMENTAL KARAKTERISTIK KUAT TEKAN DAN KARAKTERISTIK PEMBAKARAN BRIKET DAUN CENGKEH DAN JERAMI PADI

Penelitian ini mempelajari tentang karakteristik kuat tekan dan karakteristik pembakaran briket daun cengkeh dan jerami padi. Pembriketan dilakukan dengan menggunakan mesin pres hidrolik dengan tekanan pembriketan sebesar 450 kg/cm2, dengan bahan pengikat dan tanpa bahan pengikat. Bahan pengikat yang digunakan adalah lem kanji dengan kadar 5 %. Briket berbentuk silinder dengan diameter sekitar 3 cm dan tinggi 5 cm. Variasi parameter pembriketan yang digunakan adalah ukuran butir 20, 40 dan 80 mesh, kadar air 15 %, 20 % dan 25 %, serta suhu pembriketan sebesar 60 oC, 80 oC, 100 oC dan 120 oC. Uji pembakaran dilakukan dalam tungku berbentuk tabung horisontal berdiameter dalam 170 mm. Variasi perameter uji pembakaran yang digunakan adalah kecepatan aliran udara sebesar 0,6 m/s; 0,8 m/s; 1,0 m/s dan 1,2 m/s serta variasi ukuran butir sebesar 20, 40, dan 80 mesh. Suhu pembriketan berpengaruh signifikan terhadap peningkatan kuat tekan briket. Dari hasil uji pembakaran dapat ditentukan besarnya laju pembakaran, profil suhu pembakaran, nilai energi aktivasi (E ), konstanta Arrhenius (A), dan emisi CO. Dari semua percobaan, kadar emisi CO puncak lebih dari 400 ppm. Kata kunci: kuat tekan, daun cengkeh, jerami, bahan pengikat, ukuran butir, suhu pembriketan, kadar air, laju pembakaran, energi aktivasi, emisi CO.

A flexible back-contact perovskite solar micro-module

Back-contact perovskite solar cells are fabricated by depositing methylammonium lead iodide perovskite into micron-sized grooves, with opposite walls of each groove being coated with either n- or p-type selective contacts. V-Shaped grooves are created by embossing a polymeric substrate, with the different charge-selective electrodes deposited onto the walls of the groove using a directional evaporation technique. We show that individual grooves act as photovoltaic devices, having a power conversion efficiency of up to 7.3%. By series-connecting multiple grooves, we create integrated micro-modules that build open circuit voltages up to nearly 15 V and power conversion efficiencies over 4%. The devices created are fully flexible, do not include rare metals, and are processed using techniques applicable to roll-to-roll processing