Production and stabilisation of copper colloids

Imperial Users onl

Does firm size really affect earnings?

In this paper we investigate the implications of labour and capital market imperfections for the relationship between firm size and earnings. To establish that such a question is of interest we need to show that the firm size-wage effect cannot be explained by either the observed or unobserved skills of the workforce or the characteristics of the workplace. To do that we require data where controls are possible for observable time-varying firm and worker characteristics, as well as the unobservable characteristics of both the firm and its workers. Our data is a sample of workers matched with firms over time so such controls are possible. Changes in wages are shown to respond to changes both to profits per employee and the size of the firm. It is argued that these empirical results clearly reject the hypothesis that the firm-size relationship can be explained by the skills of the workers. They can be shown to be consistent with some forms of non-competitive theories of bargaining and efficiency wages.Skills, efficiency wages, bargaining, firm size, earnings, African manufacturing

Financial Risk Management in a Volatile Global Environment

The virtual collapse of several Asian markets has triggered a series of aftershocks in the global financial markets. From the alleged contagion that spread the crisis to Russia and South America to the de facto collapse of Long-Term Capital Management (LTCM), the repercussions of these events have led to endless debate. Even as participants in the global marketplace continue to seek answers to basic questions, such as the cause of the events and their implications, the public sector and industry lobbyists have offered remedies. In April 1999, the President's Working Group on Financial Markets issued a report that recommended a series of measures designed to constrain leverage in the U.S. portion of the financial system. (See Box 1) Precipitated by the collapse of LTCM, the working group saw their recommendations as a needed response to the situation leading up to capital market vulnerability, regional crises and the financial collapse of some institutions. This was followed by an industry report from the Counterparty Risk Management Group, a consortium of twelve internationally active commercial and investment banks, which was issued in June 1999. (See Box 2) The new document recommends ways to strengthen the management of market, counterparty, credit and liquidity risk without regulation and government interference. To some, the government and industry responses to the crisis that began in Malaysia and ended in the offices of the Federal Reserve Bank of New York were seen as timely. To us, they seemed premature, because neither the causes nor the effects of the tumultuous recent financial market events were well understood. To shed light on the circumstances surrounding the global crisis, and to discuss possible firm-level remedies, the Wharton Financial Institutions Center held its second Financial Engineering Roundtable on "The Measurement and Management of Global Financial Risks" last Spring in Philadelphia. The event brought together an array of distinguished academics, risk managers from the major trading houses, and financial consultants to discuss the significant issues surrounding the increased risk of today's global marketplace. In the companion papers contained in this supplement, several of the participants offer their analysis and perceptions on the events of the last year, and several others propose new risk management tools motivated by those events. Here we offer an overview of both the issues surrounding the global financial crisis, as well as the potential solutions offered to assure the stability of financial firms in the increasingly complex trading environment.

Antiscreening of the Ampere force in QED and QCD plasmas

The static forces between electric charges and currents are modified at the loop level by the presence of a plasma. While electric charges are screened, currents are not. The effective coupling constant at long distances is enhanced in both cases as compared to the vacuum, and by different amounts, a clear sign that Lorentz symmetry is broken. We investigate these effects quantitatively, first in a QED plasma and secondly using non-perturbative simulations of QCD with two light degenerate flavors of quarks.Comment: 17 pages, 8 figure

A Group of Red, Ly-alpha Emitting, High Redshift Galaxies

We have discovered two new high redshift (z=2.38) galaxies, near the previously known z=2.38 galaxy 2139-4434 B1 (Francis et al. 1996). All three galaxies are strong Ly-alpha emitters, and have much redder continuum colors (I-K about 5) than other optically-selected high redshift galaxies. We hypothesize that these three galaxies are QSO IIs; radio-quiet counterparts of high redshift radio galaxies, containing concealed QSO nuclei. The red colors are most easily modelled by an old (> 0.5 Gyr), massive (> 10E11 solar masses) stellar population. If true, this implies that at least one galaxy cluster of mass much greater than 3E11 solar masses had collapsed before redshift five.Comment: 12 pages, 2 figures, uses aaspp4 style file. Accepted for publication in Astrophysical Journal Letter

The utility of morphological, ITS molecular and combined datasets in estimating the phylogeny of the cortinarioid sequestrate fungi

Molecular technology has shown the classical, morphologically defined groupings of sequestrate cortinarioid fungi to be artificial and in need of revision. However, these same molecular studies have highlighted morphological characters, such as spore shape and ornamentation, that have proved useful for distinguishing phylogenetically informative groups. This observation underpins the hypothesis of this study: that the numeric analysis of selected morphological characters can provide the same picture of the diversity of, and relationships among, sequestrate cortinarioid fungi as that recovered from phylogenetic analysis of rDNA sequence data. Sequestrate fungi are those in which the spores mature inside an enclosed fruit body, remaining there until the fruit body decomposes or is eaten. For the purposes of this thesis the following genera are considered to contain cortinarioid sequestrate fungi: Auritella, Cortinarius, Dermocybe, Descomyces, Hymenogaster, Hysterogaster, Inocybe, Protoglossum, Quadrispora, Setchelliogaster and Timgrovea. This thesis focussed on Australian representatives of these fungi to address the hypothesis outlined above. Four analysis methods were applied to each of three datasets (morphological, rDNA and combined data) in a comparative approach to test the stated hypothesis. The four analysis methods were two multivariate methods: cluster analysis and ordination (by principal coordinates analysis), and two phylogenetic methods: maximum parsimony and Bayesian analysis. Low bootstrap support and Bayesian partition probabilities for phylogenetic analyses of the morphological data indicated this dataset had little to no phylogenetic signal discernable by parsimony and Bayesian analyses. Different analyses of the morphological data differed in the way they grouped the collections. The type of clustering method used affected the pattern of relationships recovered. The coding of the data had a much more substantial effect on the patterns of relatedness suggested by the multivariate analyses. Despite the low level of phylogenetic information and agreement between analyses of the morphological data it was found that some collections were consistently grouped together. This included the separation of the Cortinarius-like collections from the Descolea-like collections and the relatively consistent grouping of some pairs of collections and some larger groups. Thus, despite the limited phylogenetic signal of the small morphological dataset and the artefacts of coding, some relatively consistent groups were recovered. Separate analyses of the Cortinarius-, Descolea- and Hebeloma-like ITS sequences recovered similar patterns to published phylogenies. The inclusion of more sequestrate taxa and a greater sample of Australian collections than previous studies, indicated that both Timgrovea subgenera nest among the Descolea-like collections and that hitherto undiscovered lineages of Descolea-like fungi are represented among the collections in Australian herbaria. The Cortinarius-like fungi fall within clades recognised by published phylogenies. Similar topologies were supported by both Parsimony bootstrap and Bayesian partition probability values for analyses of the molecular data including the separation of Cortinarius-like collections from Descolea-like collections. However neither of these methods of analysis and evaluation yielded well-resolved deeper nodes for either of these two major clades. Comparable clades/clusters of Cortinarius- like and Descolea-like collections were found in all analyses of the molecular data. Thus phylogenetically distinct groups of cortinarioid sequestrate fungi could be consistently distinguished using ITS molecular data, but not confidently related to one another. The ratio of molecular to morphological characters (741:16) meant the patterns observed for the combined analyses were more similar to those observed in analyses of the molecular data than those of the morphological data. This included the recovery of substantially similar clades/clusters to those recovered by analyses of the molecular data alone. The value of combining the morphological and molecular data as analysed is questioned despite the congruence of the datasets according to the Incongruence-Length Difference test. Differences between the molecular and combined datasets arose primarily where the molecular data grouped collections that were also grouped by the morphological data. \ud The numeric analysis of the selected morphological characters as carried out in this study did not recover the same pattern of groups and relationships among the cortinarioid sequestrate fungi as phylogenetic analyses of ITS data. The composition of groups recovered using the morphological data alone or as part of the combined dataset, and the relationships between those groups, differed from those recovered from the molecular data alone; although there were similarities between groups recovered from different datasets. The ability of this thesis to conclusively address its fundamental hypothesis was compromised by limitations of the study such as taxon sampling, character selection, character coding and the poor resolution of the ITS phylogeny. Acknowledging these limitations, and that some similar groups were recovered, the results of this thesis do not support its stated hypothesis that the numeric analysis of selected morphological characters can provide the same picture of the diversity of, and relationships among, sequestrate cortinarioid fungi as recovered from phylogenetic analysis of rDNA sequence data

More on heavy tetraquarks in lattice QCD at almost physical pion mass

We report on our progress in studying exotic, heavy tetraquark states, $qq\prime \bar Q\bar Q\prime$. Using publicly available dynamical $n_f =2+1$ Wilson-Clover gauge configurations, generated by the PACS-CS collaboration, with pion masses $\simeq$164, 299 and 415 MeV, we extend our previous analysis to heavy quark components containing heavier than physical bottom quarks $\bar Q\bar Q\prime=\bar b\prime\bar b\prime$ or $\bar Q\bar Q\prime=\bar b\bar b\prime$, charm and bottom quarks $\bar c\bar b$ and also only charm quarks $\bar c\bar c$. Throughout we employ NRQCD and relativistic heavy quarks for the heavier than bottom, bottom and charm quarks. Using our previously established diquark-antidiquark and meson-meson operator basis we comment in particular on the dependence of the binding energy on the mass of the heavy quark component $\bar Q\bar Q$, with heavy quarks ranging from $m_Q=0.85\ldots 6.3\cdot m_b$. In the heavy flavor non-degenerate case, $\bar Q\bar Q\prime$, and especially for the tetraquark channel $ud\bar c\bar b$, we extend our work to utilize a $3\times 3$ GEVP to study the ground and threshold states thereby enabling a clear identification of possible binding. Finally, we present initial work on the $\bar Q\bar Q\prime=\bar c\bar c$ system where a much larger operator basis is available in comparison to flavor combinations with NRQCD quarks.Comment: 8 pages, 5 figures, proceedings contribution to "Lattice 2017. 35th International Symposium on Lattice Field Theory", 18th-24th June 2017, Granada, Spai

Evidence for charm-bottom tetraquarks and the mass dependence of heavy-light tetraquark states from lattice QCD

We continue our study of heavy-light four-quark states and find evidence from lattice QCD for the existence of a strong-interaction-stable $I(J^P)=0(1^+)$ $ud\bar{c}\bar{b}$ tetraquark with mass in the range of 15 to 61 MeV below $\bar{D}B^*$ threshold. Since this range includes the electromagnetic $\bar{D}B\gamma$ decay threshold, current uncertainties do not allow us to determine whether such a state would decay electromagnetically, or only weakly. We also perform a study at fixed pion mass, with NRQCD for the heavy quarks, simulating $qq^\prime \bar{b}^\prime \bar{b}$ and $q q^\prime \bar{b}^\prime\bar{b}^\prime$ tetraquarks with $q,\, q^\prime =ud$ or $\ell s$ and variable, unphysical $m_{b^\prime}$ in order to investigate the heavy mass-dependence of such tetraquark states. We find that the dependence of the binding energy follows a phenomenologically-expected form and that, though NRQCD breaks down before $m_{b^\prime}=m_c$ is reached, the results at higher $m_{b^\prime}$ clearly identify the $ud\bar{b}^\prime \bar{b}$ channel as the most likely to support a strong-interaction-stable tetraquark state at $m_{b^\prime}=m_c$. This observation serves to motivate the direct $ud\bar{c}\bar{b}$ simulation. Throughout we use dynamical $n_f=2+1$ ensembles with pion masses $m_\pi=$415, 299, and 164 MeV reaching down almost to the physical point, a relativistic heavy quark prescription for the charm quark, and NRQCD for the bottom quark(s).Comment: 24 pages, 4 figure