The Electrostatic Screening Length in Concentrated Electrolytes Increases with Concentration

According to classical electrolyte theories interactions in dilute (low ion density) electrolytes decay exponentially with distance, with the Debye screening length the characteristic length-scale. This decay length decreases monotonically with increasing ion concentration, due to effective screening of charges over short distances. Thus within the Debye model no long-range forces are expected in concentrated electrolytes. Here we reveal, using experimental detection of the interaction between two planar charged surfaces across a wide range of electrolytes, that beyond the dilute (Debye-Huuckel) regime the screening length increases with increasing concentration. The screening lengths for all electrolytes studied - including aqueous NaCl solutions, ionic liquids diluted with propylene carbonate, and pure ionic liquids - collapse onto a single curve when scaled by the dielectric constant. This non-monotonic variation of the screening length with concentration, and its generality across ionic liquids and aqueous salt solutions, demonstrates an important characteristic of concentrated electrolytes of substantial relevance from biology to energy storage.Comment: This document is the unedited authors' version of a Submitted Work that was subsequently accepted for publication in the Journal of Physical Chemistry Letters, copyright American Chemical Society, after peer review. To access the final edited and published work see http://pubsdc3.acs.org/articlesonrequest/AOR-EW6FuIC6wIh6D9qqEeH

Mapping Twitter Topic Networks: From Polarized Crowds to Community Clusters

Conversations on Twitter create networks with identifiable contours as people reply to and mention one another in their tweets. These conversational structures differ, depending on the subject and the people driving the conversation. Six structures are regularly observed: divided, unified, fragmented, clustered, and inward and outward hub and spoke structures. These are created as individuals choose whom to reply to or mention in their Twitter messages and the structures tell a story about the nature of the conversatio

Scaling analysis of the screening length in concentrated electrolytes

The interaction between charged objects in an electrolyte solution is a fundamental question in soft matter physics. It is well-known that the electrostatic contribution to the interaction energy decays exponentially with object separation. Recent measurements reveal that, contrary to the conventional wisdom given by classic Poisson-Boltzmann theory, the decay length increases with ion concentration for concentrated electrolytes and can be an order of magnitude larger than the ion diameter in ionic liquids. We derive a simple scaling theory that explains this anomalous dependence of the decay length on ion concentration. Our theory successfully collapses the decay lengths of a wide class of salts onto a single curve. A novel prediction of our theory is that the decay length increases linearly with the Bjerrum length, which we experimentally verify by surface force measurements. Moreover, we quantitatively relate the measured decay length to classic measurements of the activity coefficient in concentrated electrolytes, thus showing that the measured decay length is indeed a bulk property of the concentrated electrolyte as well as contributing a mechanistic insight into empirical activity coefficients.Comment: To appear in Physical Review Letter

The Effects of a Sugar-Sweetened Beverage Tax: Consumption, Calorie Intake, Obesity, and Tax Burden by Income

Taxing sugar-sweetened beverages has been proposed as a means to reduce calorie intake, improve diet and health, and generate revenue that governments can use to address the obesity-caused health and economic burden. Two beverage demand systems were estimated using beverage purchase data for high-income and low-income households. Using the estimated demand elasticities we examined the impacts of a hypothetical 20-percent effective tax rate (or about 0.5 cent per ounce) on beverage consumption, calorie intake, tax revenue and burden. Our results suggest that such a tax would induce an average reduction of 35 and 41 calories a day among adults and children, respectively. The tax burden is found to be regressive, although representing less than one percent of household spending on food and beverages. Tax revenue is estimated to be $5.8 billion using 2007 population estimates.beverage demand, sugar-sweetened beverage tax, soda tax, obesity, tax revenue, Agricultural and Food Policy, Consumer/Household Economics, Demand and Price Analysis, Food Consumption/Nutrition/Food Safety, Health Economics and Policy, C34, D12, Q18,

Effects of Taxing Sugar-Sweetened Beverage and Subsidizing Milk: Beverage Consumption, Nutrition, and Obesity among US Children

Taxing sugar-sweetened beverages (SSBs) has been proposed as a means to improve U.S. diet and health and generate revenue to address obesity-related issues. A related concern is that children’s intake of SSBs, a third that of milk consumption in the late 1970s, now equals milk consumption. Displacing milk by SSBs may shortchange the buildup of bone mass, increasing the risk of fractures and osteoporosis in later life. Accordingly, we examine the effects that a 20- percent SSB tax and a 20-percent milk price subsidy would have on the diet and health of American children. We estimated US beverage demand systems and used the estimated demand elasticities to examine the impacts of the hypothetical SSB tax and milk subsidy. Our results suggest that a 20-percent tax-induced increase in soda price alone would reduce calorie intakes by 40 calories a day among children, lowering the obesity rate from 16.1 percent to 13.4 percent and the overweight rate from 32 percent to 26.9 percent. When a 20-percent price subsidy for milk is bundled with the SSB tax, children would on average decrease their calorie intake (21 calories a day) and increase their calcium intake, but the overweight and obesity rates would actually increase by around 2 percent. The seemingly contradiction between the two averages, lower calories and higher obesity, is due to the fact that the majority of children (90 percent) remain unchanged in their weight classification under the price interventions but on average reduce their calorie intake. Six percent of children increase their calorie intake and gain enough weight to cross the overweight threshold, whereas four percent of children decrease their calorie intake to improve from being overweight to healthy weight. Therefore, when averaging the effects of the price interventions, we found a decrease in calorie intake and higher overweight and obesity rates.Sugar-sweetened beverages (SSB), soda tax, milk subsidy, beverage demand, and obesity, Agricultural and Food Policy, Consumer/Household Economics, Demand and Price Analysis, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, Health Economics and Policy, C30, D12, Q18,

Taxing Caloric Sweetened Beverages: Potential Effects on Beverage Consumption, Calorie Intake, and Obesity

The link between high U.S. obesity rates and the overconsumption of added sugars, largely from sodas and fruit drinks, has prompted public calls for a tax on caloric sweetened beverages. Faced with such a tax, consumers may reduce consumption of these sweetened beverages and substitute nontaxed beverages, such as bottled water, juice, and milk. This study estimated that a tax-induced 20-percent price increase on caloric sweetened beverages could cause an average reduction of 37 calories per day, or 3.8 pounds of body weight over a year, for adults and an average of 43 calories per day, or 4.5 pounds over a year, for children. Given these reductions in calorie consumption, results show an estimated decline in adult overweight prevalence (66.9 to 62.4 percent) and obesity prevalence (33.4 to 30.4 percent), as well as the child at-risk-for-overweight prevalence (32.3 to 27.0 percent) and the overweight prevalence (16.6 to 13.7 percent). Actual impacts would depend on many factors, including how the tax is reflected in consumer prices and the competitive strategies of beverage manufacturers and food retailers.Sugar-sweetened beverages (SSB), soft drinks, soda tax, added sugars, obesity, and beverage demand, Food Consumption/Nutrition/Food Safety, Health Economics and Policy,

Northwest Africa 11522: A New Paired Stone of Martian Polymict Regolith Breccia Northwest Africa 7034

No abstract available

Coherent Imaging Spectroscopy of a Quantum Many-Body Spin System

Quantum simulators, in which well controlled quantum systems are used to reproduce the dynamics of less understood ones, have the potential to explore physics that is inaccessible to modeling with classical computers. However, checking the results of such simulations will also become classically intractable as system sizes increase. In this work, we introduce and implement a coherent imaging spectroscopic technique to validate a quantum simulation, much as magnetic resonance imaging exposes structure in condensed matter. We use this method to determine the energy levels and interaction strengths of a fully-connected quantum many-body system. Additionally, we directly measure the size of the critical energy gap near a quantum phase transition. We expect this general technique to become an important verification tool for quantum simulators once experiments advance beyond proof-of-principle demonstrations and exceed the resources of conventional computers