bluuebunny/crossref_metadata_2025 huggingface dataset:
On the equivalence of a countable disjoint class of sets of positive measure and a weaker condition than total σ–finiteness of measures
Authors: Ficker V.
Published: April 2009

Let (X, S) be a measurable space and S be a σ-algebra of subsets of X. A nonempty class M is said to be a class of null sets if M ⊂ S, M is closed under countable unions of sets and E ∩ F ∈ M whenever E ∈ M and F ∈ S. It is possible to show that such concepts as absolute continuity, singularity and independence of measures can be studied simply by classes of null sets and that similar results can be obtained under the condition that each disjoint subclass of S – M is countable, denoted (S – M)C. If (X, S,μ) is a measure space then M = {E ∈ S: μ(E) = O} is a class of null sets of S and S – M the class of all sets of positive measure. We say that a measure μ has the property σ if there exists a sequence of totally finite measures on S such that σ(E) = for all E ∈ S. This property of measures is weaker than total σ–finiteness of measures. The main result of the present paper is as follows: Let (X, S,μ) be a measure space and M = {E ∈ S: μ(E) = O}. Then (S – M)C if and only if μ has the property σ.
A constructive proof of Gelbaum's theorem on tensor products
Authors: Robbins David A.
Published: April 2009

A constructive proof is given of Gelbaum's result that the maximal ideal space of the tensor product of commutative Banach algebras is homeomorphic to the cartesian product of the maximal ideal spaces.
Axioms for constructive fields
Authors: Staples John
Published: April 2009

In constructive mathematics the Dedekind cut definition of real number is not equivalent to the definition of real number by Cauchy sequences, and the Dedekind real numbers do not satisfy Heyting's axioms for constructive fields. A more general notion of constructive field is proposed which includes the Dedekind real numbers; some linear algebra is given which applies to such fields.
Rudin-Shapiro sequences on compact groups
Authors: Figà-Talamanca Alessandro , Price J.F.
Published: April 2009

The existence of a certain type of Rudin-Shapiro sequence of functions is shown for all infinite compact groups which are not Lie, thus extending a recent result of the authors to all infinite compact groups.
On Conway's conjecture for integer sets
Authors: Macdonald Sheila Oates , Street Anne Penfold
Published: April 2009

Let A = {ai} be a finite set of integers and let p, m denote the orders of A + A = {ai+aj} and A – A = {ai–aj} respectively. J.H. Conway conjectured that p ≤ m always and that p = m only if A is symmetric about 0. This conjecture has since been disproved; here we make several other observations on the values of p and m.
The response of lake levels to an unsteady wind stress
Authors: Noye B.J.
Published: April 2009

This paper presents a theoretical investigation into the forced oscillations produced in an elongated lake by wind stresses varying in time. Analysis of the appropriate hydrodynamical equations of motion, in the absence of friction, and the equation of continuity give an estimate of the response function of the longitudinal component of the wind stress onto water level. Two mathematical models are used, one giving an analytical solution and the other requiring numerical methods for solution. The first model assumes that the lake is a homogeneous rectangular body of water and the second uses the mean depth h(x) and area of cross section A(x), considered as functions of distance x directed along the longitudinal axis of the lake.
Finiteness conditions in soluble groups and Lie algebras
Authors: Stewart Ian N.
Published: April 2009

We prove some new theorems and reprove some old ones about finitely generated soluble groups and Lie algebras by a uniform method. Among the applications are Gruenberg's Theorem on Engel groups, for which we obtain a very short proof; and the Milnor and Wolf polynomial growth theorem. It is shown that a finitely generated soluble group with all 2-generator subgroups polycyclic is itself polycyclic, and that a finitely generated soluble Lie algebra, all of whose inner derivations are algebraic, is finite-dimensional. This last result enables us to give a partial answer to a question of Jacobson.
A supernilpotent non-special radical class
Authors: van Leeuwen L.C.A. , Jenkins T.L.
Published: April 2009

Let F be the upper radical determined by all fields. The supernilpotent radical classes which are not special have thus far always contained F properly. The purpose of this note is to construct a countably infinite number of supernilpotent radical classes which are not special and each of which is properly contained in F. The construction involves a ring due to Leavitt which is interesting in its own right and is not generally known. All rings considered are associative.
Free generators in free inverse semigroups: Corrigenda
Authors: Reilly N.R.
Published: April 2009

In [1], Theorem 2.2, a necessary and sufficient condition is given for a subset of an inverse semigroup to generate a free inverse subsemigroup. However one very obvious further condition is omitted. The result should read as follows.
A tauberian theorem related to the modified Hankel transform
Authors: Soni Kusum , Soni R.P.
Published: April 2009

The modified Hankel transform arises naturally in connection with certain semigroup operations on measures in probability theory. We give a tauberian theorem for this transform when certain higher moments exist. The probabilistic significance of our result is that it translates a regularity condition on the transform into a direct condition on the measure. This complements earlier results by Pitman and Bingham for the trigonometric and the modified Hankel transform respectively.
On perturbed stochastic discrete systems
Authors: Pachpatte B.G.
Published: April 2009

The object of this paper is to study a stochastic discrete system, including an operator T, of the form

as a perturbation of the linear stochastic discrete system

where ω ∈ Ω, the supporting set of probability measure space (Ω, A, P) and n ∈ N, the set of nonnegative integers. We are concerned vith the existence, uniqueness, boundedness, and asymptotic behavior of random solutions of the above equation.
Error bounds in the approximation of functions
Authors: Sahney Badri N. , Gopal Rao V. Venu
Published: April 2009

Let f(x) ε Lipα, 0 < α < 1, in the range (-π, π), and periodic with period 2π, outside this range. Also let

.

We define the norm as

and let the degree of approximation be given by

where Tn (x) is some n–th trigonometric polynomial.
A finite set covering theorem II
Authors: Brace Alan , Daykin D.E.
Published: April 2009

Let n, s, t be integers with s > t > 1 and n > (t+2)2s–t–1. We prove that if n subsets of a set S with s elements have intersection I and union J then some t of them have intersection J and union J. The result is best possible.
A characterization of generalized Hall planes
Authors: Johnson N.L.
Published: April 2009

We prove that a translation plane π of odd order is a generalized Hall plane if and only if π is derived from a translation plane of semi-translation class 1–3a. Also, a derivable translation plane of even order and class 1–3a derives a generalized Hall plane. We also show that the generalized Hall planes of Kirkpatrick form a subclass of the class of planes derived from the Dickson semifield planes.
Projective groups in varieties
Authors: Bryce R.A.
Published: April 2009

A number of questions of Philip Hall concerning complemented normal subgroups of finite relatively free groups are considered.
A remark on Ribenboim's paper ‘On the extension of orders in ordered modules’
Authors: Spoerel D.
Published: April 2009

We give another formulation of Theorem 1 of Ribenboim's paper, Bull. Austral. Math. Soc. 2 (1970), 81–88. Our condition on a module to be totally ordered such that this order extends a given strict order seems to be more useful for applications than condition (2) of Ribenboim. This is shown for example in Corollaries 3 and It of our paper. Corollary 4 is due to Ribenboim. Corollary 3 generalizes the corresponding well known result on abelian groups.
A finite set covering theorem III
Authors: Brace Alan , Daykin D.E.
Published: April 2009

Let n, s, t be integers with s > t > 2. If a family of n different subsets of a set S, with s elements, has the properties,
(i) each member belongs to a set of (t+1) members which together have union S,
(ii) no member belongs to a set of t members which together have union S,
then we prove that n ≤ (t+1)s−t−1. The result is best possible.
Existence of a bounded approximate identity in a tensor product
Authors: Robbins David A.
Published: April 2009

It has been shown that the existence of a (left) approximate identity in the tensor product A ⊗ B of Banach algebras A and B, where α is an admissible algebra norm on A ⊗ B, implies the existence of approximate identities in A and B. The question has been raised as to whether the boundedness of the approximate identity in A ⊗αB implies the boundedness of the approximate identities in A and B. This paper answers the question affirmatively with a being the greatest cross-norm.
On the differential equation for the conventional tide-well system
Authors: Noye B.J.
Published: April 2009

This paper discusses solutions to the differential equation

which governs the height

of the non-dimensional water level inside a conventional tide-well when the corresponding height of the sea-level outside is X(τ). A perturbation solution correct to O(β4), for small β, for the particular case X = sinτ described previously has been extended to O(β6) for any function X(τ) differentiable at least three times. Two special cases, where X(τ) is a single sinusoid and the sum of two sinusoids, are treated in detail.
The multiplicator of a regular product of groups
Authors: Haebich William , Cossey P.J.
Published: April 2009

It is shown that ifGis an arbitrary regular product of its subgroupsAλ, ∈ ϵI, then the multiplicator,M(G), is the director product of theM(Aλ) together with a certain other group. This extends a calculation ofM(A1×A2) due to Schur. As an application, we find the multiplicator of a vertai wreath productAwrVBwhereAis abelian. A representing group for a finite regular product is also constructed.
Representation of a function in terms of its mean boundary values
Authors: Ching Chin-Hung , Chui Charles K.
Published: April 2009

We give the representation formula of a function in a disc in terms of its arithmetic means on the boundary. We also give applications of this formula to the solutions of some elementary differential equations with prescribed means of boundary or initial data.
Uniqueness and nonuniqueness in mean boundary value problems
Authors: Ching Chin-Hung , Chui Charles K.
Published: April 2009

We give some sufficient conditions to guarantee the uniqueness of certain mean boundary value problems for a circle. Also we show that, in general, we cannot expect uniqueness of the problem for an arc unless the function is analytic in a neighborhood of the unit circle or some shifted means of the function are also known.
Subnormal structure in some classes of infinite groups
Authors: McCaughan D.J.
Published: April 2009

Let p be a prime and G a group with a p–reduced nilpotent normal subgroup N such that G/N is a nilpotent p–group. It is shown that if G has the subnormal intersection property and if G/N is finite or N is p–torsion-free, then G is nilpotent. This result is used to prove that an abelian-by-finite group has the subnormal intersection property if and only if it has a bound for the subnormal indices of its subnormal subgroups.
A commutativity theorem for power-associative rings
Authors: Outcalt D. L. , Yaqub Adil
Published: April 2009

Let R be a power-associative ring with identity and let I be an ideal of R such that R/I is a finite field and x ≡ y (mod I) implies x2 = y2 or both x and y commute with all elements of I. It is proven that R must then be commutative. Examples are given to show that R need not be commutative if various parts of the hypothesis are dropped or if “x2 = y2” is replaced by “xk = yk” for any integer k > 2.
A note on simultaneous approximation
Authors: Mack J. M.
Published: April 2009

We observe that good simultaneous rational approximations to given rationally dependent real numbers must satisfy the same rational dependence relationships as do the given numbers.
An elementary proof of part of a classical conjecture
Authors: Gaudet R. J. , Gamlen J. L. B.
Published: April 2009

An elementary proof is given for the Lp conjecture, p > 2, which states that for a locally compact group G, Lp (G) (p > 2) is closed under convolution if and only if G is compact.
Locally finite varieties of groups arising from Cross varieties
Authors: Macdonald Sheila Oates
Published: April 2009

Let be a Cross variety and let n be the least integer such that (n) is locally finite; then n ≤ 2d + 3 where d is an upper bound for the number of generators of certain critical groups in .
Maximal sum-free sets in finite abelian groups
Authors: Yap H.P.
Published: April 2009

Maximal sum-free sets in elementary abelian 3-groups and groups G = Z3 ⊕ Z3 ⊕ Zp where p is a prime congruent to 1 modulo 3 are completely characterized.
Functions of asymptotic expansions
Authors: Brown A. , Dancer E.N.
Published: April 2009

The paper extends a theorem given by Entringer on the asymptotic expansion of a composite function.
On prime noninvertible links
Authors: Whitten Wilbur
Published: April 2009

It is the purpose of this paper to exhibit an infinite collection of prime, noninvertible links; each link in the collection is the union of two invertible knots. In fact, we present two such families of links. Our examples heuristically indicate that collections of links of this type exist in many varieties.
A finitely generated, infinitely related group with trivial multiplicator
Authors: Baumslag Gilbert
Published: April 2009

We exhibit a 3-generator metabelian group which is not finitely related but has a trivial multiplicator.

1. The purpose of this note is to establish the exitense of a finitely generated group which is not finitely related, but whose multiplecator is finitely generated. This settles negatively a question whichb has been open for a few years (it was first brought to my attention by Michel Kervaire and Joan Landman Dyer in 1964, but I believe it is somewhat older). The group is given in the follwing theorem.
An arithmetic remark on entire periodic functions
Authors: Mahler Kurt
Published: April 2009

For every positive number w, there exists an odd entire transcendental function

.

with rational integral coefficients ah such that f〈z+w〉 = f〈z〉.
A note on generalized characters
Authors: Bryant R.M. , Kovács L.G.
Published: April 2009

Let α be a generalized character of a (not necessarily finite) group G over an arbitrary field, and n a positive integer. It is shown that the function α(n) defined by α(n) (g) = α(gn) is also a generalized character of G. An application confirms a conjecture of Robert Higgins and David Ballew: if G is finite and k is also a positive integer, the k-th power of the number of n-th roots of g, summed over all g in G, is divisible by the order of G.
Construction of strongly regular graphs using affine designs: Corrigenda
Authors: Wallis W.D.
Published: April 2009

There is a numerical error in the statement of Theorem 1 of [1]. The expression

which occurs in (6) must be replaced by

and a similar change must be made in line 5 of page 46. As a consequence, equation (7) must be changed to

and the definition of x to

in the statement of Theorem 2. These changes are purely arithmetical, and do not entail any further changes in the paper.
Correlated Order Flow: Pervasiveness, Sources, and Pricing Effects
Authors: Harford Jarrad , Kaul Aditya
Published: April 2009

We examine the importance of indexing, industry, and broad market forces in driving common effects in order flow, returns, and trading costs. Common effects are strong for order flow and returns in a sample of S&P 500 stocks, but are weak in a sample of non-index stocks and for trading costs in both samples. Industry and broad market effects exist in order flow for both samples, but indexing effects are dominant. Correlated order flow drives common effects in returns and, to a lesser extent, those in trading costs. An event study of the effect of index addition on order flow and return comovement reinforces these conclusions. Our results show that common effects are not pervasive and have implications for diversification strategies and price formation models.
The Performance of Alternative Interest Rate Risk Measures and Immunization Strategies under a Heath-Jarrow-Morton Framework
Authors: Agca Senay
Published: April 2009

Using a Monte Carlo simulation, this study addresses the question of how traditional risk measures and immunization strategies perform when the term structure evolves in a Heath-Jarrow-Morton (1992) manner. The results suggest that, for immunization purposes, immunization strategies and portfolio formation strategies are more important than interest rate risk measures. The performance of immunization strategies depends more on the transaction costs and the holding period than on the risk measures. Moreover, the immunization performance of bullet and barbell portfolios is not very sensitive to interest rate risk measures.
Stealth Trading in Options Markets
Authors: Anand Amber , Chakravarty Sugato
Published: April 2009

We investigate how price discovery occurs in the options markets through traders' trade size choice. By employing transactions data on all options traded on a sample of 100 firms, we show that informed traders fragment their orders into small (medium) trades for low (high) volume contracts. We also find that almost 60% of the price discovery occurs in the exchange with the largest market share for a given option, where informed traders favor medium size trades. Upon examining distinct option series for a given stock, we find that at-the-money calls display the highest information share.
The Declining Information Content of Dividend Announcements and the Effects of Institutional Holdings
Authors: Amihud Yakov , Li Kefei
Published: April 2009

We propose an explanation for the “disappearing dividend” phenomenon: a decline in the information content of dividend announcements, which reduces the propensity of firms to use dividends as a costly signal. A reason for a decline in the information content of dividends is the rise in holdings by institutional investors that are more sophisticated and informed. Indeed, we find a decline in CAR at dividend change announcements since the mid–1970s. Across firms, CAR is a decreasing function of institutional holdings. Institutional investors exploit their superior information and buy before dividend increases. In addition, dividends are less likely to rise in firms with high institutional holdings.
Monte Carlo Valuation of American Options through Computation of the Optimal Exercise Frontier
Authors: Ibáñez Alfredo , Zapatero Fernando
Published: April 2009

This paper introduces a Monte Carlo simulation method for pricing multidimensional American options based on the computation of the optimal exercise frontier. We consider Bermudan options that can be exercised at a finite number of times and compute the optimal exercise frontier recursively. We show that for every date of possible exercise, any single point of the optimal exercise frontier is a fixed point of a simple algorithm. Once the frontier is computed, we use plain vanilla Monte Carlo simulation to price the option and obtain a low-biased estimator. We illustrate the method with applications to several types of options.
Bullish/Bearish Strategies of Trading: A Nonlinear Equilibrium
Authors: Dridi Ramdan , Germain Laurent
Published: April 2009

We study a financial market where risk-neutral traders are endowed with a signal that perfectly reveals the direction (but not the exact amount) of the liquidation value of a normally distributed risky asset. The impact of order flow on prices is nonlinear with a bullish/bearish information structure, which is broadly consistent with empirical evidence. Also, private information is revealed quicker than in a strategic oligopoly.
Missed Opportunities: Optimal Investment Timing When Information is Costly
Authors: Guthrie Graeme
Published: April 2009

Real option analysis typically assumes that projects are continuously evaluated and launched at precisely the time determined to be optimal, but real world projects cannot be managed in this way because of the costs of formally evaluating an investment opportunity. This paper shows that immediate investment is more attractive if evaluation costs are high or the amount of information to be revealed by an evaluation is large. The optimal delay until a reevaluation is long if evaluation costs are high or the amount of information to be revealed by an evaluation is small. The reduction in the value of project rights is especially severe when the value of the completed project is strongly mean reverting because then precision in investment timing is particularly important.
Do Market Timing Hedge Funds Time the Market?
Authors: Chen Yong , Liang Bing
Published: April 2009

This paper examines whether self-described market timing hedge funds have the ability to time the U.S. equity market. We propose a new measure for timing return and volatility jointly that relates fund returns to the squared Sharpe ratio of the market portfolio. Using a sample of 221 market timing funds during 1994–2005, we find evidence of timing ability at both the aggregate and fund levels. Timing ability appears relatively strong in bear and volatile market conditions. Our findings are robust to other explanations, including public information-based strategies, options trading, and illiquid holdings. Bootstrap analysis shows that the evidence is unlikely to be attributed to luck.
A Yen is Not a Yen: TIBOR/LIBOR and the Determinants of the Japan Premium
Authors: Covrig Vicentiu , Low Buen Sin , Melvin Michael
Published: April 2009

Pricing in the euroyen market is based on LIBOR, the London Interbank Offered Rate, set at 11:00AM London time or TIBOR, the Tokyo Interbank Offered Rate, set at 11:00AM Tokyo time. The changing TIBOR-LIBOR spread reflects the credit risk associated with Japanese banks or the “Japan premium”. The spread is modeled as a function of determinants of bank default and firm value. Systematic variation in the spread can be explained by interest rate and stock price effects along with public information flows of good and bad news regarding Japanese banking, with a separate role for bank credit downgrades and upgrades.
Irreversible Investment, Financing, and Bankruptcy Decisions in an Oligopoly
Authors: Jou Jyh-bang , Lee Tan
Published: April 2009

This paper examines a firm's debt level, investment timing, and investment scale choices in a continuous-time model where the output price of a good that the firm produces depends on a stochastic demand-shift variable and the total industry supply of the good. Using the simple symmetric Cournot-Nash equilibrium assumption that all firms are identical and therefore follow the same financing and investment strategies, we show that competition decreases the output price and hence encourages a firm to wait for a higher demand level before it is profitable to invest. We also demonstrate how uncertainty, bankruptcy costs, and corporate taxation affect the firm's financing and investment decisions.
Shifting the diurnal cycle of parameterized deep convection over land
Authors: Rio C. , Hourdin F. , Grandpeix J.‐Y. , Lafore J.‐P.
Published: April 2009

In most atmospheric circulation models used for climate projections, cloud and convective processes are not explicitly resolved but parameterized. Such models are known to produce a diurnal cycle of continental thunderstorms in phase with insolation, while observed precipitation peaks in late afternoon. We propose a new approach which corrects this long standing bias of parameterized convection. In this approach, deep convection triggering and intensity are controlled by sub‐cloud processes: here boundary layer thermals and gust fronts, and potentially orography or surface heterogeneities. The representation of the diurnal cycle of deep convection is greatly improved in 1D mode, with rainfall maximum delayed from midday to late afternoon, provided parameterizations account for the key role played by shallow cumulus in preconditioning deep convection and by gust fronts in the self‐sustaining of thunderstorms in the afternoon.
Synoptic classification of Moderate Resolution Imaging Spectroradiometer aerosols over Israel
Authors: Carmona I. , Alpert P.
Published: April 2009

The origins and variety of aerosols in Israel are strongly influenced by synoptic conditions as well as other variables. Days affected by a weak Persian trough system are characterized by coarse aerosols from North Africa, which contain mainly mineral dust aerosols, whereas days affected by the Red Sea trough with an eastern axis are characterized by fine aerosols from northern Europe. Some synoptic systems contain both groups of aerosols as well as mixed aerosols, e.g., the Red Sea trough with a central axis. This study utilizes the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra Satellite to obtain a synoptic classification of aerosols over Israel for 6 years. MODIS synoptic classification revealed a number of different aerosol types. For weak Persian trough, a high from the west and a medium Persian trough, the MODIS Terra aerosol optical thickness (AOT) fine mode fractions are 0.51, 0.54, and 0.51, respectively. While for Red Sea trough with an eastern or central axis AOT fine mode fraction (‘f’) is higher and is equal to 0.63 and 0.59, respectively. This is the first study in the region that investigates average back trajectory with regards to both synoptic systems and aerosol type. Investigation of back trajectories for the Persian trough synoptic system indicates that days with low ‘f’ at 700 hPa are associated with flows from North Africa, while days with high ‘f’ are linked to flow from Europe. Most of our findings are not unexpected, but provide the first 6 years quantified aerosol classification which is based on the synoptic systems.
On the effects of divide migration, along‐ridge flow, and basal sliding on isochrones near an ice divide
Authors: Martín Carlos , Hindmarsh Richard C. A. , Navarro Francisco J.
Published: April 2009

Radar layer geometry in divide areas is strongly influenced by the operation of the Raymond effect, which causes upwarping of the layers as a consequence of the nonlinear rheology of ice. The detailed geometry of these layers is known to store a record of change in the cryosphere, of local thinning, and of the age of formation of the divide and has been surmised to provide information about lateral motion of divides. Such lateral motion can be caused by changes in flanking ice streams, and the divide area thereby contains a record of ice stream dynamics. It has also been suggested that a large perturbation of divide position will obliterate the cumulative effects of the operation of the Raymond mechanism, leading to the disappearance of Raymond bumps. Since the Raymond effect has a strong influence on the age‐depth relation in ice cores, knowledge of whether its operation is localized (leading to strong bump formation) or distributed is crucial in the interpretation of ice cores. The detailed evolution of ice divide radar layer geometry remains poorly understood. Employing a full thermomechanically coupled transient model, we qualitatively explore the effect of divide migration on radar layer geometry. Certain qualitative features emerge which can be used to infer history of cryosphere change, in particular, in areas distant from the usual sites of geological dating. There remains uncertainty about the influence of sliding on the operation of the Raymond effect. Under certain conditions, the existence of sliding can damp or eliminate the operation of the Raymond effect. If this is generally true, then dating of ice divides may simply be a date for the freezing of the divide bottom. We show that sliding does not necessarily eliminate the formation of bumps. Dates of divide formation are likely to be dates for the location of the ridge at a particular spot. Raymond bump evolution is weakened by flow along the ridge. We explore quantitatively the strength of this effect, using a scaling analysis to show that the weakening can efficiently be described by one parameter, the ratio of along‐ridge slope to a measure of the across‐divide curvature.
Response of bed surface patchiness to reductions in sediment supply
Authors: Nelson Peter A. , Venditti Jeremy G. , Dietrich William E. , Kirchner James W. , Ikeda Hiroshi , Iseya Fujiko , Sklar Leonard S.
Published: April 2009

River beds are often arranged into patches of similar grain size and sorting. Patches can be distinguished into “free patches,” which are zones of sorted material that move freely, such as bed load sheets; “forced patches,” which are areas of sorting forced by topographic controls; and “fixed patches” of bed material rendered immobile through localized coarsening that remain fairly persistent through time. Two sets of flume experiments (one using bimodal, sand‐rich sediment and the other using unimodal, sand‐free sediment) are used to explore how fixed and free patches respond to stepwise reductions in sediment supply. At high sediment supply, migrating bed load sheets formed even in unimodal, sand‐free sediment, yet grain interactions visibly played a central role in their formation. In both sets of experiments, reductions in supply led to the development of fixed coarse patches, which expanded at the expense of finer, more mobile patches, narrowing the zone of active bed load transport and leading to the eventual disappearance of migrating bed load sheets. Reductions in sediment supply decreased the migration rate of bed load sheets and increased the spacing between successive sheets. One‐dimensional morphodynamic models of river channel beds generally are not designed to capture the observed variability, but should be capable of capturing the time‐averaged character of the channel. When applied to our experiments, a 1‐D morphodynamic model (RTe‐bookAgDegNormGravMixPW.xls) predicted the bed load flux well, but overpredicted slope changes and was unable to predict the substantial variability in bed load flux (and load grain size) because of the migration of mobile patches. Our results suggest that (1) the distribution of free and fixed patches is primarily a function of sediment supply, (2) the dynamics of bed load sheets are primarily scaled by sediment supply, (3) channels with reduced sediment supply may inherently be unable to transport sediment uniformly across their width, and (4) cross‐stream variability in shear stress and grain size can produce potentially large errors in width‐averaged sediment flux calculations.
Seasonal methylmercury dynamics in water draining three beaver impoundments of varying age
Authors: Roy Virginie , Amyot Marc , Carignan Richard
Published: April 2009

We monitored water chemistry including unfiltered and filtered total mercury (THg), total methylmercury (TMeHg) and redox‐sensitive species in three beaver pond inlets and outlets in southwestern Quebec (Canada) on a monthly basis from March to September 2007. In‐pond methylation efficiencies (percent of THg as TMeHg) peaked when ponds were ice‐covered (%TMeHg/THg range: 53–80%) and in summer (%TMeHg/THg range: 34–67%). Low oxygen concentrations during these periods likely promoted reducing conditions leading to inorganic mercury methylation. Total dissolved MeHg was the predominant fraction of TMeHg in outlets (80% on average), and TMeHg values were up to 27–fold higher in outlets compared to inlets in summer. During the summer, TMeHg concentrations (up to 2.80 ng L−1) were higher in the recent pond than in the older ones. Seasons and pond age influence MeHg production dynamic in beaver ponds; beaver pond formation may increase MeHg transfer through food webs within the pond area and in downstream aquatic systems.
Midnight temperature maximum (MTM) in Whole Atmosphere Model (WAM) simulations
Authors: Akmaev R. A. , Wu F. , Fuller‐Rowell T. J. , Wang H.
Published: April 2009

Discovered almost four decades ago, the midnight temperature maximum (MTM) with typical magnitudes of 50–100 K has been regularly observed by satellite and ground‐based instruments in the tropical upper thermosphere. Although several mechanisms have been suggested to explain the phenomenon, previous attempts to reproduce it with comprehensive thermosphere‐ionosphere models have been unsuccessful. First long‐term simulations with the Whole Atmosphere Model (WAM) reveal the presence of a realistically prominent MTM and reproduce the salient features of its daily, seasonal, and latitudinal variability. Preliminary analysis indicates that the feature may be traced down to the lower thermosphere, where it is manifested primarily in the form of an upward propagating terdiurnal tidal wave. Its spectrum expands to higher‐order zonal wavenumbers and frequencies and its phase advances to near midnight higher up in the thermosphere. Possible mechanisms generating this wave may involve nonlinear interactions between other tidal harmonics originating in the middle and lower atmosphere. Our results thus suggest that the MTM is yet another phenomenon driven by dynamical links between the lower and upper atmosphere and ionosphere.
Stereoscopic imaging of an Earth‐impacting solar coronal mass ejection: A major milestone for the STEREO mission
Authors: Davis C. J. , Davies J. A. , Lockwood M. , Rouillard A. P. , Eyles C. J. , Harrison R. A.
Published: April 2009

We present stereoscopic images of an Earth‐impacting Coronal Mass Ejection (CME). The CME was imaged by the Heliospheric Imagers onboard the twin STEREO spacecraft during December 2008. The apparent acceleration of the CME is used to provide independent estimates of its speed and direction from the two spacecraft. Three distinct signatures within the CME were all found to be closely Earth‐directed. At the time that the CME was predicted to pass the ACE spacecraft, in‐situ observations contained a typical CME signature. At Earth, ground‐based magnetometer observations showed a small but widespread sudden response to the compression of the geomagnetic cavity at CME impact. In this case, STEREO could have given warning of CME impact at least 24 hours in advance. These stereoscopic observations represent a significant milestone for the STEREO mission and have significant potential for improving operational space weather forecasting.
Structural basis of N‐end rule substrate recognition in Escherichia coli by the ClpAP adaptor protein ClpS
Authors: Schuenemann Verena J , Kralik Stephanie M , Albrecht Reinhard , Spall Sukhdeep K , Truscott Kaye N , Dougan David A , Zeth Kornelius
Published: April 2009

In Escherichia coli, the ClpAP protease, together with the adaptor protein ClpS, is responsible for the degradation of proteins bearing an amino‐terminal destabilizing amino acid (N‐degron). Here, we determined the three‐dimensional structures of ClpS in complex with three peptides, each having a different destabilizing residue—Leu, Phe or Trp—at its N terminus. All peptides, regardless of the identity of their N‐terminal residue, are bound in a surface pocket on ClpS in a stereo‐specific manner. Several highly conserved residues in this binding pocket interact directly with the backbone of the N‐degron peptide and hence are crucial for the binding of all N‐degrons. By contrast, two hydrophobic residues define the volume of the binding pocket and influence the specificity of ClpS. Taken together, our data suggest that ClpS has been optimized for the binding and delivery of N‐degrons containing an N‐terminal Phe or Leu.
Tandem-mirror success leads to expanded MFTF
Authors: Schwarzschild Bertram M.
Published: April 2009

Two ideas advanced in recent years for improving the confinement of plasmas in mirror machines have added much to the promise of such devices as potential fusion-power reactors. In an experiment just completed at Livermore, the tandem-mirror configuration, first suggested in 1976, appears to have passed its first major experimental test with colors flying.1 The more recently proposed thermal-barrier idea, which is expected to strengthen the confinement capabilities of the tandem configuration, will undergo its first experimental trial next year at this same, Tandem Mirror Experimental Facility (TMX).
CESR shows bare-bottomed mesons
Authors: Schwarzschild Bertram M.
Published: April 2009

In its first year of operation, the Cornell electron–positron storage ring, CESR, has provided strong evidence for the existence of a fifth quark flavor. The three narrow upsilon mesonic states near 10 GeV, first seen at Fermilab in 1977 and 1978, had offered the initial experimental evidence for a hadronic building block heavier than the charmed quark (see PHYSICS TODAY, October 1977, page 17 and January 1979, page 17). The Γ, Γ′ and Γ″ were generally believed to be bound states of a massive new “bottom” quark, b, and its antiparticle.
Toward better acoustics for concert halls
Authors: Schroeder Manfred R.
Published: April 2009

Concert-hall acoustics are governed by the meshing of two sets of problems: on the one hand the physical problems of wave propagation and attenuation in irregularly bounded spaces and, on the other hand, the psychological problems of how the human listener perceives the sounds impinging on his ears and what he prefers to hear.
Biological membranes
Authors: Chance Britton , Mueller Paul , De Vault Don , Powers L.
Published: April 2009

For solid-state physicists and engineers the “ultimate in miniaturization” would be to produce devices with structures that are about 8 or 10 nm across—about a tenth of the smallest scale that can currently be produced. (See PHYSICS TODAY, November 1979, page 25.) Biological systems, however, have, in a sense, solved the problems associated with such small microstructures. The fundamental unit of many cell functions, the lipid bilayer membrane (figure 1), is 4 nm thick; in regions where the membrane carries proteins it may be as much as 10 nm thick. Other elements of the cell, such as the microtubules that provide its structural framework, have similar dimensions.
Photon-stimulated desorption selectively breaks bonds
Authors: Lubkin Gloria B.
Published: April 2009

A perennial nuisance to experimenters is electron-stimulated desorption, in which adsorbed atoms leave the surface of a material being struck by electrons. Over the past several years, this widely observed phenomenon has been undergoing development as a tool for studying chemical bonding at single-crystal surfaces between specific kinds of atoms and at defect sites. Last year the existence of photon-stimulated desorption was demonstrated. These techniques can selectively break specific surface bonds and be used to identify bonding sites and bond angles.
Great undersea waves may be solitons
Authors: Schwarzschild Bertram M.
Published: April 2009

Peculiar striations more than a hundred kilometers long, visible on satellite pictures of the surface of the Andaman and Sulu Seas in the Far East, appear to be of interest in fields as far removed from oceanogaphy as quantum field theory. A recent report of underwater current and temperature variations associated with such surface phenomena in the Andaman Sea, by Alfred Osborne, a physicist at Exxon Production Research (Houston), and Terrence Burch, an oceanographer with EG&G Environmental Consultants (Waltham, Mass.), suggests that these striations mark the propagation of “solitons,” exotic solutions of nonlinear wave equations that have captured the interest of mathematical physicists studying a broad range of phenomena spanning 22 orders of magnitude in size.
Laser-induced chemical processes
Authors: Letokhov V. S.
Published: April 2009

Proposals for controlling or inducing chemical reactions with laser light have been around almost as long as lasers themselves. Immediately after Theodore Maiman's invention of the ruby laser in 1960 and Ali Javan, William Bennett and Donald Herriott's invention of the helium–neon gas laser in 1961 suggestions for using this new type of light source in chemical processes followed. The proposals resulted essentially from adapting already well-known principles of photochemistry. Yet almost no research employing lasers in chemistry was done for ten years. Not until tunable lasers and high-powered infrared lasers arrived at the end of the 1960's and in the early 1970's did laser chemistry become experimentally feasible, and the period since then has seen intense and systematic study of atomic and molecular processes. Of particular interest are those selective processes applicable to laser isotope separation, such as the work on carbon isotopes carried out in the apparatus shown in figure 1 and discussed later in this article. Selective processes also appear to be useful for the production of highly pure substances and for the study of certain photobiochemical compounds. In this article I will be able to give only a brief survey of the great amount of work currently in progress, concentrating particularly on those aspects being studied at laboratories in the Soviet Union.
State-to-state reaction dynamics
Authors: Zare Richard N. , Bernstein Richard B.
Published: April 2009

The study of chemical reaction kinetics can be likened to the task of making a motion picture of a reaction. The trouble thus far with achieving this goal seems to be the problem of too many would-be actors who strut upon the stage without proper cue and mumble their lines too rapidly to be understood—for chemical reactions occur with the ease of striking a match and at a speed so fast (on a subpicosecond time scale for the making of new bonds and breaking of old ones) as to be a severe challenge to the moviemaker who would like to record individual frames.
Studies with crossed laser and molecular beams
Authors: Lee Yuan T. , Shen Y. Ron
Published: April 2009

During the last twenty years sophisticated microscopic experimental techniques and large-scale theoretical computations have significantly enhanced our understanding of the detailed dynamics of chemical reactions. The development of computer codes to perform lengthy and detailed computations has made it possible to clarify the connection between the first principles of quantum chemistry and the behavior of substances in the real world. Modern spectroscopy, laser technology and molecular-beam methods allow us to observe chemical reactions on the atomic and molecular levels in great detail.
Fitch and Cronin share Nobel prize for CP violation
Authors: Lubkin Gloria B.
Published: April 2009

“For the discovery of violations of fundamental symmetry principles in the decay of neutral K mesons,” the Royal Swedish Academy of Sciences has awarded the 1980 Nobel Prize in Physics to James W. Cronin of the University of Chicago and Val L. Fitch of Princeton University. This year the prize is worth $210 000.
Sandia to use light ions for fusion
Authors: Schwarzschild Bertram M.
Published: April 2009

It would presumably take an order of magnitude less beam energy to run an inertial-confinement thermonuclear reactor with ion beams than with electron beams. But until last year the technological problems of producing and focusing a sufficiently intense light-ion beam have kept the emphasis of particle-beam fusion research on electron-beam devices. The largest particle-beam fusion machines, at Sandia in Albuquerque and at the Kurchatov Institute in Moscow (still under construction), were originally designed to implode deuterium-tritium pellets with beams of 2-MeV electrons.
Ballistic heat pulses in crystals
Authors: Wolfe James P.
Published: April 2009

The physics of phonons, or elastic waves, with gigahertz to terahertz frequencies is currently gaining considerable attention. A variety of new phonon techniques has been developed over the past few years as a result of new technologies and materials; they include notable advances in the generation of tunable monochromatic phonon beams at terahertz frequencies, in the creation of “phonon optics” devices such as reflection gratings for ultrasonic waves, and in the interaction of high-frequency phonons with impurities and free carriers in semiconductors. This recent activity was particularly evident at the Third International Conference on Phonon Scattering in Condensed Matter held last year at Brown University.
Black-hole thermodynamics
Authors: Bekenstein Jacob D.
Published: April 2009

To the physicist casually interested in gravitation, a black hole is a passive object that swallows anything near it and cannot be made to disgorge it; it absorbs but cannot emit. At the close of the last decade the experts shared this view. Recently, however, this simple picture has changed entirely. Perhaps no single development highlighted more the new views about black holes than the quantum argument presented by Stephen Hawking of Cambridge University in 1974 that a black hole must radiate spontaneously with a thermal spectrum. The importance of this phenomenon is not so much in possible practical applications, not even in its astrophysical implications, but rather in that it has confirmed earlier suspicions that gravitation, thermodynamics and the quantum world are deeply interconnected. This connection, which might be symbolized by the thermodynamic engine shown in figure 1, engenders hope that we may achieve a synthesis of these three branches of physics in our time and bears witness to the profound unity of physics, a unity too often veiled in an age of increasing specialization.
Theory of defect processes
Authors: Stoneham A. Marshall
Published: April 2009

Most scientific studies of imperfect solids concentrate on the properties of individual isolated defects. Such properties include their electronic structure, as shown by optical and spin-resonance data, formation energies, and diffusion parameters. Yet these properties alone do not always determine those practical applications of solid-state physics that exploit the behavior of defects. The principal extra ingredients can often be described as defect processes—how defects interact with each other and how the imperfect lattice evolves. That is, the time-dependent behavior of the imperfect solid, not just its static properties, affects how it can be used.
Pulsed molecular-beam sources
Authors: Scott John T.
Published: April 2009

A new type of fast, pulsed molecular-beam source for collision studies and molecular spectroscopy appears to have several advantages over the traditional continuous-flow sources. It improves signal-to-noise in the detectors, produces very “cold” beams with little or no rotational or vibrational excitation, and it allows good time-of-flight measurements to determine velocity spectra. The source was developed by W. Ronald Gentry and Clayton Giese at the University of Minnesota. Their work employs two such sources to investigate collisions between two molecular beams.
Efficient use of energy revisited
Authors: Ross Marc
Published: April 2009

In the past several years everyone has become considerably more aware of the problems of energy supply and demand. Although extensive resources of energy are available in principle, energy that is both cheap to extract and cheap to use—such as the oil and natural gas to which we have become accustomed—is very limited. The rising cost of all forms of energy is only one of the problems we associate with the provision and use of energy. The uncertainty of existing supplies—as illustrated by the Iranian revolution and by the accident at Three Mile Island—is another, though related, problem. A different kind of problem is in the development of new supplies (fluid fuels from coal, oil from shale, nuclear breeder reactors, for example); here, necessary steps in the development may be slow in coming or even unsuccessful.