The Viking rocket: A memoir

The development and testing of the Viking rocket series is reviewed. These twelve sounding rockets were launched from 1949 to 1954

Geodetic, teleseismic, and strong motion constraints on slip from recent southern Peru subduction zone earthquakes

We use seismic and geodetic data both jointly and separately to constrain coseismic slip from the 12 November 1996 M_w 7.7 and 23 June 2001 M_w 8.5 southern Peru subduction zone earthquakes, as well as two large aftershocks following the 2001 earthquake on 26 June and 7 July 2001. We use all available data in our inversions: GPS, interferometric synthetic aperture radar (InSAR) from the ERS-1, ERS-2, JERS, and RADARSAT-1 satellites, and seismic data from teleseismic and strong motion stations. Our two-dimensional slip models derived from only teleseismic body waves from South American subduction zone earthquakes with M_w > 7.5 do not reliably predict available geodetic data. In particular, we find significant differences in the distribution of slip for the 2001 earthquake from models that use only seismic (teleseismic and two strong motion stations) or geodetic (InSAR and GPS) data. The differences might be related to postseismic deformation or, more likely, the different sensitivities of the teleseismic and geodetic data to coseismic rupture properties. The earthquakes studied here follow the pattern of earthquake directivity along the coast of western South America, north of 5°S, earthquakes rupture to the north; south of about 12°S, directivity is southerly; and in between, earthquakes are bilateral. The predicted deformation at the Arequipa GPS station from the seismic-only slip model for the 7 July 2001 aftershock is not consistent with significant preseismic motion

Mutual learning in a tree parity machine and its application to cryptography

Mutual learning of a pair of tree parity machines with continuous and discrete weight vectors is studied analytically. The analysis is based on a mapping procedure that maps the mutual learning in tree parity machines onto mutual learning in noisy perceptrons. The stationary solution of the mutual learning in the case of continuous tree parity machines depends on the learning rate where a phase transition from partial to full synchronization is observed. In the discrete case the learning process is based on a finite increment and a full synchronized state is achieved in a finite number of steps. The synchronization of discrete parity machines is introduced in order to construct an ephemeral key-exchange protocol. The dynamic learning of a third tree parity machine (an attacker) that tries to imitate one of the two machines while the two still update their weight vectors is also analyzed. In particular, the synchronization times of the naive attacker and the flipping attacker recently introduced in [1] are analyzed. All analytical results are found to be in good agreement with simulation results

Vortex ratchet reversal: The role of interstitial vortices

Triangular arrays of Ni nanotriangles embedded in superconducting Nb films exhibit unexpected dynamical vortex effects. Collective pinning with a vortex lattice configuration different from the expected fundamental triangular "Abrikosov state" is found. The vortex motion which prevails against the triangular periodic potential is produced by channelling effects between triangles. Interstitial vortices coexisting with pinned vortices in this asymmetric potential, lead to ratchet reversal, i.e. a DC output voltage which changes sign with the amplitude of an applied alternating drive current. In this landscape, ratchet reversal is always observed at all magnetic fields (all numbers of vortices) and at different temperatures. The ratchet reversal is unambiguously connected to the presence of two locations for the vortices: interstitial and above the artificial pinning sites.Comment: 21 pages, 4 figures, 1 Tabl

Is There a Role for Lawyers in Preventing Future Enrons

Following the collapse of the Enron Corporation, the ethical obligations of corporate attorneys have received increased scrutiny. The Sarbanes-Oxley Act of 2002, enacted in response to calls for corporate reform, specifically requires the Securities and Exchange Commission to address the lawyer’s role by requiring covered attorneys to “report up” evidence of corporate wrongdoing to key corporate officers, and, in some circumstances, to the board of directors. Failure to “report up” subjects a lawyer to liability under federal law. This Article argues that the reporting up requirement reflects a second-best approach to corporate governance reform. Rather than focusing on the actors that traditionally control a corporation’s activities, the statute attempts to solve governance problems indirectly by assigning to the lawyer the role of corporate gatekeeper and information intermediary. We demonstrate that the reporting up requirement fails to address the incentives that motivate corporate attorneys, directors and managers. At the same time, the provision threatens to undermine the flow of information between lawyers and corporate actors. As a consequence, we suggest that the requirement is unlikely to achieve its objective of providing key corporate decision makers with early information about potential misconduct. Moreover, attorney and manager responses to the reporting up requirement are likely to reduce the quality of legal services provided to the corporation. Based on this cost-benefit analysis, we conclude that the Sarbanes-Oxley approach to corporate governance reform is flawed. Instead, we argue that a demand side approach is more likely to realign corporate attorney incentives and to reinvigorate the business lawyer’s important role in promoting good corporate governance. Toward that end, we identify specific reforms tailored to increasing the incentives for corporate officers and directors to demand and obtain better legal advice

Is There a Role for Lawyers in Preventing Future Enrons?

Following the collapse of the Enron Corporation, the ethical obligations of corporate attorneys have received increased scrutiny. The Sarbanes-Oxley Act of 2002, enacted in response to calls for corporate reform, specifically requires the Securities and Exchange Commission to address the lawyer’s role by requiring covered attorneys to “report up” evidence of corporate wrongdoing to key corporate officers, and, in some circumstances, to the board of directors. Failure to “report up” subjects a lawyer to liability under federal law. This Article argues that the reporting up requirement reflects a second-best approach to corporate governance reform. Rather than focusing on the actors that traditionally control a corporation’s activities, the statute attempts to solve governance problems indirectly by assigning to the lawyer the role of corporate gatekeeper and information intermediary. We demonstrate that the reporting up requirement fails to address the incentives that motivate corporate attorneys, directors and managers. At the same time, the provision threatens to undermine the flow of information between lawyers and corporate actors. As a consequence, we suggest that the requirement is unlikely to achieve its objective of providing key corporate decision makers with early information about potential misconduct. Moreover, attorney and manager responses to the reporting up requirement are likely to reduce the quality of legal services provided to the corporation. Based on this cost-benefit analysis, we conclude that the Sarbanes-Oxley approach to corporate governance reform is flawed. Instead, we argue that a demand side approach is more likely to realign corporate attorney incentives and to reinvigorate the business lawyer’s important role in promoting good corporate governance. Toward that end, we identify specific reforms tailored to increasing the incentives for corporate officers and directors to demand and obtain better legal advice

Cohesin cleavage by separase is enhanced by a substrate motif distinct from the cleavage site.

Chromosome segregation begins when the cysteine protease, separase, cleaves the Scc1 subunit of cohesin at the metaphase-to-anaphase transition. Separase is inhibited prior to metaphase by the tightly bound securin protein, which contains a pseudosubstrate motif that blocks the separase active site. To investigate separase substrate specificity and regulation, here we develop a system for producing recombinant, securin-free human separase. Using this enzyme, we identify an LPE motif on the Scc1 substrate that is distinct from the cleavage site and is required for rapid and specific substrate cleavage. Securin also contains a conserved LPE motif, and we provide evidence that this sequence blocks separase engagement of the Scc1 LPE motif. Our results suggest that rapid cohesin cleavage by separase requires a substrate docking interaction outside the active site. This interaction is blocked by securin, providing a second mechanism by which securin inhibits cohesin cleavage

Surface roughness of aesthetic restorative materials: an in vitro comparison

KIMThe purpose of this study was to compare the surface roughness of three types of aesthetic restorative material. Six standard samples of two brands of each type of material were prepared namely: hybrid composites (Prodigy, Z100), compomers (Compoglass F, Hytac Aplitip) and glass ionomer cements (Photac-Fil, Vitremer) in a perspex mould (N = 36). Upper and lower surfaces were covered with Mylar strips which, in turn, were covered with glass slides and compressed to express excess material. After light curing, specimens were stored in distilled water for 14 days. Thereafter, one side of each specimen was polished sequentially with medium, fine and super fine Soflex discs (treatment). Untreated surfaces served as controls. All surfaces were examined with Talysurf and the surface roughness (Ra) of each specimen was recorded. Three measurements were made of each specimen. A 4-way ANOVA and Tukey's Studentised range test were used to analyse the data. Statistically significant effects were found for both type of material (P = 0.0001) and for treatment process (P = 0.0065). Among unpolished specimens: Compoglass F is significantly rougher than Vitremer, Z100, Prodigy and Hytac Aplitip, and compomers are significantly rougher than hybrids. Among polished specimens: Photac-Fil is significantly rougher than Z100 but does not differ from Compoglass F, Vitremer, Prodigy and Hytac Aplitip, and glass ionomers are also significantly rougher than hybrids. The smoothest surface is obtained when curing materials against a Mylar strip