The Cuba Library

Concepts and implementation of the Cuba library for multidimensional numerical integration are elucidated.Comment: 6 pages. Talk given at the X International Workshop on Advanced Computing and Analysis Techniques in Physics Research, ACAT 2005, DESY-Zeuthen, Germany, 22-27 May 200

Doubly Spinning Black Rings

We study a method to solve stationary axisymmetric vacuum Einstein equations numerically. As an illustration, the five-dimensional doubly spinning black rings that have two independent angular momenta are formulated in a way suitable for fully nonlinear numerical method. Expanding for small second angular velocity, the formulation is solved perturbatively upto second order involving the backreaction from the second spin. The obtained solutions are regular without conical singularity, and the physical properties are discussed with the phase diagram of the reduced entropy vs the reduced angular momenta. Possible extensions of the present approach to constructing the higher dimensional version of black ring and the ring with the cosmological constant are also discussed.Comment: 20 pages, 6 figure

Geographical distribution and aspects of the ecology of the hemiparasitic angiosperm Striga asiatica (L) Kuntze: A herbarium study

Striga asiatica (Scrophulariaceae) is an obligate root hemiparasite of mainly C-4 grasses (including cereals). It is the most widespread of the 42 Striga species occurring in many semi-tropical, semi-arid regions of mainly the Old World. Examination of herbaria specimens revealed that S. asiatica has a wider geographical distribution, is present at higher altitudes and occurs in a more diverse range of habitats than previously reported. The host range is also larger than previously reported and is likely to include a large number of C-3 plants. Morphology of examined specimens revealed variation in size and corolla colour suggesting the existence of ecotypes. Climate may exert a significant influence on the distribution of S. asiatica given the diversity of potential host plants and their distribution beyond the current recorded range of S. asiatica

Using the Output Embedding to Improve Language Models

We study the topmost weight matrix of neural network language models. We show that this matrix constitutes a valid word embedding. When training language models, we recommend tying the input embedding and this output embedding. We analyze the resulting update rules and show that the tied embedding evolves in a more similar way to the output embedding than to the input embedding in the untied model. We also offer a new method of regularizing the output embedding. Our methods lead to a significant reduction in perplexity, as we are able to show on a variety of neural network language models. Finally, we show that weight tying can reduce the size of neural translation models to less than half of their original size without harming their performance.Comment: To appear in EACL 201

Earth models consistent with geophysical data

Earth models consistent with geophysical data using Monte Carlo metho

Energy Alarmism: The Myths That Make Americans Worry about Oil

Many Americans have lost confidence in their country's "energy security" over the past several years. Because the United States is a net oil importer, and a substantial one at that, concerns about energy security naturally raise foreign policy questions. Some foreign policy analysts fear that dwindling global oil reserves are increasingly concentrated in politically unstable regions, and they call for increased U.S. efforts to stabilize -- or, alternatively, democratize -- the politically tumultuous oil-producing regions. Others allege that China is pursuing a strategy to "lock up" the world's remaining oil supplies through long-term purchase agreements and aggressive diplomacy, so they counsel that the United States outmaneuver Beijing in the "geopolitics of oil." Finally, many analysts suggest that even the "normal" political disruptions that occasionally occur in oil-producing regions (e.g., occasional wars and revolutions) hurt Americans by disrupting supply and creating price spikes. U.S. military forces, those analysts claim, are needed to enhance peace and stability in crucial oil-producing regions, particularly the Persian Gulf. Each of those fears about oil supplies is exaggerated, and none should be a focus of U.S. foreign or military policy. "Peak oil" predictions about the impending decline in global rates of oil production are based on scant evidence and dubious models of how the oil market responds to scarcity. In fact, even though oil supplies will increasingly come from unstable regions, investment to reduce the costs of finding and extracting oil is a better response to that political instability than trying to fix the political problems of faraway countries. Furthermore, Chinese efforts to lock up supplies with long-term contracts will at worst be economically neutral for the United States and may even be advantageous. The main danger stemming from China's energy policy is that current U.S. fears may become a self-fulfilling prophecy of Sino-U.S. conflict. Finally, political instability in the Persian Gulf poses surprisingly few energy security dangers, and U.S. military presence there actually exacerbates problems rather than helps to solve them. Our overarching message is simply that market forces, modified by the cartel behavior of OPEC, determine most of the key factors that affect oil supply and prices. The United States does not need to be militarily active or confrontational to allow the oil market to function, to allow oil to get to consumers, or to ensure access in coming decades