Time filter

Source Type

Xian, China

Qu J.,China Three Gorges University | Zou L.,China Three Gorges University | Zhang J.,Normal University
Proceedings 2010 IEEE International Conference on Information Theory and Information Security, ICITIS 2010 | Year: 2010

In this paper, we propose a practical dynamic multi-secret sharing scheme based on the intractability of the discrete logarithm and one way hash functions, the exclusive OR operation. Security analysis shows that our scheme could correctly reconstruct the shared secret, and our scheme is as secure as Lin-Yeh's scheme. In addition, in our schemes, all participants themselves select their shares, so the calculation amount of dealer is reduced and secure channel between the dealer and any participant is avoided. The group secret combiner can verify whether each participant's pseudo secret share true or not. © 2010 IEEE. Source

Cui S.-W.,Normal University | Zhu R.-Z.,CAS Institute of Mechanics | Wang X.-S.,Henan Polytechnic University | Yang H.-X.,Cangzhou Normal University Library | And 2 more authors.
Wuli Xuebao/Acta Physica Sinica | Year: 2015

Theoretical analyses are given to the known approaches of nano-contact angle and arrive at the conclusions: 1) All the approaches based on the assumptions of Qusi-uniform liquid film, or uniform liquid molecular density, or uniform liquid molecular densities respectively inside and outside the interface layer cannot give the correct nano-contact angle, and it is difficult to improve them. Among these approaches, both the conclusions of nano-contact angle sure being 0° and sure being 180° are false. 2) Density functional theory (DFT) approach and Molecular Dynamics (MD) approach are capable to treat of nano-contact angle, however, the work is very heavy for using the DFT approach. 3) In 1995, Ruzeng Zhu (College Physic [Vol. 14 (2), p1-4 (in Chinese)], corrected the concept of contact angle in a earlier false theory for macro contact angle and obtained the most simple and convenient approximate formula of nano-contact angle α = (1-2EPS/EPL) π, where EPL is the potential of a liquid molecule in the internal liquid and EPS is the interact potential between a liquid molecule and the solid on which it locats. Both EPS and EPL can be obtained by MD, therefore this theory as a approximate simplified form belongs to Molecular Dynamics approach of nano-contact angle. The results of 0° and 180° for complete wetting and complete non-wetting given by this formula are correct under the assumption of incompressible fluid, therefore, this theory is worthy of further development. For this end, based on the physical analysis, we assume that the potential energy of a liquid molecule on the Gibss surface of tension outside the three-phase contact area is EPL/2x and that of a liquid molecule on the three-phase contact line is (1+kEPS/EPL) αEPL/2xπ, where x and k are optimal parameters. According to the condition that the potential energy is the same everywhere on the Gibss surface of tension, an improved approximate formula for nano-contact angle α = π (1-2xEPS/EPL)/(1+kEPS/EPL) is obtained. To obtain the value of x and k, MD simulations are carried on argon liquid cylinders placed on the solid surface under the temperature 90 K, by using the lennard - Jones (LJ) potentials for the interaction between liquid molecules and for that between a liquid molecule and a solid molecule with the variable coefficient of strength a. Eight values of a between 0.650 and 0.825 are used. The Gibss surfaces of tension are obtained by simulations and their bottom angles are treated as the approximate nano-contact angles. Combining these data with the physical conditions (when EPS/EPL = 0, α=π), the optimized parameter values x=0.7141, k=1.6051 with the correlation coefficient 0.9997 are obtained by least square method. This correlation coefficient close enough to 1 indicates that for nano liquid solid contact system with different interaction strength, the parameter of optimization x and k really can be viewed as constants, so that our using MD simulation to determine of the optimized parameters is feasible and our approximate formula is of general applicability. ©, 2015, Chinese Physical Society. All right reserved. Source

Home > Press > Quantum effects affect the best superconductor: Quantum effects explain why hydrogen sulphide is a superconductor at record-breaking temperatures Abstract: The theoretical results of a piece of international research published in Nature, whose first author is Ion Errea, a researcher at the UPV/EHU and DIPC, suggest that the quantum nature of hydrogen (in other words, the possibility of it behaving like a particle or a wave) considerably affects the structural properties of hydrogen-rich compounds (potential room-temperature superconducting substances). This is in fact the case of the superconductor hydrogen sulphide: a stinking compound that smells of rotten eggs, which when subjected to pressures a million times higher than atmospheric pressure, behaves like a superconductor at the highest temperature ever identified. This new advance in understanding the physics of high-temperature superconductivity could help to drive forward progress in the search for room-temperature superconductors, which could be used in levitating trains or next-generation supercomputers, for example. Superconductors are materials that carry electrical current with zero electrical resistance. Conventional or low-temperature ones behave that way only when the substance is cooled down to temperatures close to absolute zero (-273 °C o 0 degrees Kelvin). Last year, however, German researchers identified the high-temperature superconducting properties of hydrogen sulphide which makes it the superconductor at the highest temperature ever discovered: -70 °C or 203 K. The structure of the chemical bonds between atoms changes In classical or Newtonian physics it is possible to measure the position and momentum of a moving object to determine where it is going and how long it will take to reach its destination. These two properties are inherently linked. However, in the strange world of quantum physics, it is impossible, according to Heisenberg's uncertainty principle, for specific pairs of observable complementary physical magnitudes of a particle to be known at the same time. Hydrogen is the lightest element in the periodic table, so it is an atom that is very strongly affected by quantum behaviour. Its quantum nature affects the structural and physical properties of various hydrogen compounds. An example is high-pressure ice where quantum fluctuations of the proton lead to a change in the way the molecules are held together, due to the fact that the chemical bonds between atoms end up being symmetrical. The researchers in this study believe that a similar quantum hydrogen-bond symmetrisation occurs in the hydrogen sulphide superconductor. The researchers have formulated the calculations by considering the hydrogen atoms as quantum particles behaving like waves, and they have concluded that they form symmetrical bonds at a pressure similar to that used experimentally by the German researchers. So they have succeeded in explaining the phenomenon of superconductivity at record-breaking temperatures because in previous calculations hydrogen atoms were treated as classical particles, which made impossible to explain the experiment. All this highlights the fact that quantum physics and symmetrical hydrogen bonds lie behind high-temperature conductivity in hydrogen sulphide. The researchers are delighted that the good results obtained in this research show that quantitative predictions and computation can be used with complete confidence to speed up the discovery of high-temperature superconductors. According to the calculations made, the quantum symmetrisation of the hydrogen bonds has a great impact on the vibrational and superconducting properties of hydrogen sulphide. "In order to theoretically reproduce the observed pressure dependence of the superconducting critical temperature, the quantum symmetrisation needs to be taken into account," explained Ion Errea, the lead researcher in the study. This theoretical study shows that in hydrogen-rich compounds, the quantum motion of hydrogen can strongly affect the structural properties (even modifying the chemical bonding), as well as the electron-phonon interaction that drives the superconducting transition. In the view of the researchers, theory and computation have played a key role in the search for superconducting hydrides subjected to extreme compression. And they also pointed out that in the future an attempt will be made to increase the temperature until room-temperature superconductivity is achieved while dramatically reducing the pressures required. ### Additional information This international research was carried out with the collaboration of researchers from the UPV/EHU-University of the Basque Country and Donostia International Physics Center (DIPC), the UPMC Université Paris 06 (Sorbonne), the University of Cambridge (Cavendish Laboratory), the Jiangsu Normal University, the Carnegie Institution of Washington, Jilin University, and the University of Rome 'La Sapienza'. The lead researcher in the study was Ion Errea (Donostia-San Sebastian, 1984); he is a PhD holder in Physics and is currently a researcher at DIPC and a lecturer in the UPV/EHU's Department of Applied Physics. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

News Article | December 19, 2014
Site: www.bloomberg.com

When Bill Gross quit bond giant Pacific Investment Management Co. three months ago, almost as stunning as his departure was his choice of employer: Janus Capital Group Inc., a struggling stock fund manager whose assets had shrunk by half from a peak 14 years earlier. Two chief executive officers had tried and failed to turn around the firm. A third, Richard M. Weil, a former Pimco operating chief who had worked with Gross before moving to Janus, started to diversify, yet redemptions persisted. When Gross asked to run a new, popular type of bond fund for Janus, Weil knew it may be the break he had been looking for. “Bill Gross is our Peyton Manning, that game-changing level of talent for us,” Weil said in an interview in Denver, referring to the quarterback of the National Football League’s Denver Broncos. “People are looking at us.” Hiring Gross was the boldest step yet in an almost five-year effort by Weil to attract new money and change the public perception of Janus, a firm still known primarily for its growth-equity funds. Earlier this year, he hired Nobel laureate Myron Scholes as chief investment strategist to help develop asset allocation products, which have gained popularity in recent years. And he bought a company that runs exchange-traded funds, a rapidly expanding area of the industry, and plans to start an ETF run by Gross. Janus shares surged 43 percent on Sept. 26, their biggest one-day gain ever, after Janus announced that Gross would join the firm. They have almost tripled in the past three years as Weil added strategies and slowed the exodus of money managers. “Since Dick’s arrival, he’s done a number of interesting things and they’re starting to take shape,” said Macrae Sykes, an analyst at Gabelli & Co. in Rye, New York, who recommends investors buy Janus shares. “You’re starting to see some nice fruit from his ascension.” Turning around an asset manager isn’t easy because investors don’t easily forget when they lose money. It took Legg Mason Inc. seven years to stanch redemptions sparked by poor performance prior to and during the 2008 financial crisis. Janus has suffered redemptions for 21 straight quarters, and assets, at $174 billion at the end of the third quarter, remain 48 percent below their peak in 2000. While the fourth quarter may be the first in which clients are adding money on a net basis again, Gross so far has only attracted a small fraction of the billions that clients pulled from Pimco after his departure. Gross is facing a challenging market as slumping oil prices and a crisis in Russia rattle markets. His Janus Global fund has declined 0.8 percent since Gross took over, beating 59 percent of its peers from Oct. 6 through yesterday, according to data from Chicago-based research firm Morningstar Inc. Weil’s plans for Janus are ambitious. He has expanded offerings beyond Janus’s traditional focus on domestic stocks, and plans to triple the proportion invested in fixed income and adding asset-allocation products. Along with Ashwin Alankar, head of asset allocation and risk management, Scholes is running products designed to help clients target how much risk they want to take. Scholes and Alankar are developing quantitative models to indicate when investors should shift their holdings between asset classes. Scholes, the co-originator of the Black-Scholes options pricing model, shared the Nobel Prize with Robert Merton in 1997 for his work on valuing derivatives. He was a partner in Long-Term Capital Management LP, the hedge fund whose $4 billion loss in 1998 set off a near-panic in financial markets. In what Weil calls a “happy confluence” of events, Gross joined just as Janus announced the acquisition of VelocityShares, to expand in exchange-traded products, where industrywide assets have more than tripled to $1.9 trillion since 2008, according to the Investment Company Institute. “Bill has opened the door for us to be very relevant in product wrappers like closed-end funds and ETFs,” Kelly Hagg, the head of product development, said in an e-mail. “Our first ETF will be a Bill Gross-run strategy and we are currently working with our internal product development team and the new VelocityShares team to develop the most compelling strategy for the market.” VelocityShares will open ETFs in strategies including fixed income, asset allocation and volatility management, said Hagg. The first strategy probably won’t replicate Gross’s Unconstrained fund, he said. Janus’s first ETF may be more of a traditional fixed income strategy, according to a person with knowledge of the matter, who asked not to be identified because the details are private. The firm’s sales team met on Dec. 10 to plan how to roll out new products, the person said. Janus asked the U.S. Securities and Exchange Commission yesterday for permission to “establish certain index based market basket investment products,” according to a filing. The funds would be able to invest as much as 20 percent in index futures, options, swaps or derivatives, according to the filing. To support Gross, Janus is building its infrastructure, adding as many as eight people to help in pricing and processing derivative and volatility trades, Weil said. The firm is also hiring at least one investment professional to assist Gross. In addition, Janus plans to hire as many as five people to its fixed-income team over the next year, as client deposits expand funds. October and November made for the first two-month stretch of net inflows since April 2010, the firm said. Analysts are divided on Janus’s outlook, with more than half of those surveyed by Bloomberg recommending that investors hold the shares, and a quarter advising that clients sell. Janus, which bet heavily on riskier growth companies before the collapse of technology stocks at the turn of the century, had seen assets peak at $334 billion in August 2000. The next year, the firm was one of the first mutual-fund companies identified by former New York Attorney General Eliot Spitzer as permitting improper trading, and agreed to pay $226 million in penalties and management fee cuts to settle complaints. Steven L. Scheid took over as Janus’s CEO in 2004 as he set out to restore client confidence after the mutual fund scandal. He relinquished his role as CEO to Gary Black in 2006, while remaining chairman of the board. Redemptions persisted under Black, whose tenure was also marked by manager departures. At least 15 fund managers and senior executives departed after Black reorganized and cut the influence and pay of star fund managers. Scheid, who retired in April 2012 after eight years, clashed with fund managers over the company’s leadership, and passed on takeover attempts by larger rivals. The company conducted talks with Franklin Resources Inc., the San Mateo, California-based money manager, and Massachusetts Mutual Life Insurance Co. in 2009 over a possible purchase of Janus, two people familiar with the matter said at the time. Weil, 51, took over as CEO in February 2010 after about 15 years at Pimco, most recently running the unit that advises investors on valuation and risk management. He was a member of its executive committee, and served as general counsel from 1999 to 2000, when he became chief operating officer. He took home $20.3 million in 2010, his first year at Janus, including $10 million in stock received as a signing bonus. In 2013, Weil was paid $4.7 million, according to company filings. Now, approaching his five-year anniversary at Janus, the top priority is performance for clients, Weil said. Janus funds on average beat 52 percent of peers over the past five years through Dec. 17, and 50 percent over 15 years, according to data from Morningstar. This year, they’re ahead of 58 percent. Employee turnover has slowed, with 11 money managers and leaders leaving Janus’s equity business and one from fixed-income since 2010. Janus has replaced seven of those equity managers and has hired two in fixed income. Weil also reduced the reliance on equities, with just over 80 percent of Janus’s assets now in actively-managed equities, compared with 92 percent at the end of 2009. Adding such a high-level name as Gross created anxiety for the existing fixed-income team at Janus, led by Gibson Smith, who joined in 2001. The day Janus announced that Gross was joining, Smith’s team peered into his office in shock. He was on the phone, smiling. “Everyone thought I was dead, shot,” he said. He and Weil called the more than 30 fixed-income professionals into their corner conference room to explain that Gross would add to the existing bond team rather than replace it. “The way Dick and I are talking about it -- separate and distinct, but complementary,” Smith said. “Even with all the drama associated, what a win for Janus.” Weil said he plans to keep the two bond platforms separate. “Gibson is more traditional; he invests in cash bonds, builds up from credit,” while Gross trades more derivatives, he said. “They’re good for each other. Neither has to do what the other is doing.” That separation is made easier because Gross is working just down the block from Newport Beach, California-based Pimco, rather than moving to Denver. He flew in last month to speak to a gathering of Janus investment professionals, in a room set up like a college lecture hall. For 40 minutes, he discussed the history of trade and took questions for another 20 minutes. Gross’s long-term performance is among the best in the industry, with his main fund at Pimco beating 96 percent of peers over 15 years, according to Morningstar. Pimco’s assets doubled to $2 trillion between 2010 and 2013. Janus has been winning new cash since Gross joined the firm. Gross’s Janus Global Unconstrained Bond Fund received an estimated $769 million in new money last month, bringing assets to $1.21 billion, according to data compiled by Bloomberg. The firm also won a $500 million mandate from a vehicle managed by George Soros’s investment firm. Janus Flexible Bond got about $125 million of net deposits. That fund is beating 48 percent of peers this year, according to data compiled by Bloomberg. As Janus’s employees enjoy the spotlight, money manager Andy Acker remembers how, when he joined the firm 15 years ago, people were lining up at Janus’s investor service center on 100 Fillmore Street, waiting to invest in the firm’s funds. “I want people to experience what I experienced when I first started. I want to get back to that, winning -- a place everyone pays attention to.”

Zhenhua C.,Normal University | Zhenhua C.,Xian University of Science and Technology | Shundong L.,Normal University | Qianhong W.,Beihang University | Qiong H.,South China Agricultural University
Security and Communication Networks | Year: 2015

In this paper, a distributed secret share update scheme with public verifiability for ad hoc network is proposed, in which the system secret key is collaboratively generated by k nodes or more, instead of by a centralized key generation center. To prevent a passive adversary from collecting other nodes' shares to compromise the system key over a long period, each node can periodically refresh its share without changing the system key. At the same time, to resist an active adversary to forge partial share and even to solve the accusation problem, any one can publicly verify the correctness of partial shares submitted by other nodes in the share update phase. To achieve our goals, we explore the technique of verifiable encryption with additive homomorphism and that of threshold cryptography. The analysis shows that the proposed scheme is more secure and efficient than the previous schemes for ad hoc networks. © 2014 John Wiley & Sons, Ltd. Source

Discover hidden collaborations