500 Kilovolt Cathode Rays

The high potential x-ray tube at the California Institute has been modified so as to permit either x-rays or cathode rays to be produced. Electron currents up to 35 microamperes have been obtained through an aluminum window. A typical magnetic velocity spectrum of the high speed electrons passing out of an aluminum window is presented. The high velocity limit corresponds to about 500 kilovolts when the transformer voltage is 600 kilovolts peak. The velocity spectrum appears to be continuous and no absorption anomalies due to aluminum and lead foil are evident. The time required to obtain a velocity spectrum was reduced to a few minutes by allowing the electrons after being magnetically deflected, to pass through a copper foil into the air. The outside of the foil is coated with calcium tungstate and the photographic plate is placed in contact with the tungstate. It is noted that part of the photographic action of the high speed electrons is due to fluorescence of the glass backing of the photographic plates

500 Kilovolt Cathode Rays

The high potential x-ray tube at the California Institute has been modified so as to permit either x-rays or cathode rays to be produced. Electron currents up to 35 microamperes have been obtained through an aluminum window. A typical magnetic velocity spectrum of the high speed electrons passing out of an aluminum window is presented. The high velocity limit corresponds to about 500 kilovolts when the transformer voltage is 600 kilovolts peak. The velocity spectrum appears to be continuous and no absorption anomalies due to aluminum and lead foil are evident. The time required to obtain a velocity spectrum was reduced to a few minutes by allowing the electrons after being magnetically deflected, to pass through a copper foil into the air. The outside of the foil is coated with calcium tungstate and the photographic plate is placed in contact with the tungstate. It is noted that part of the photographic action of the high speed electrons is due to fluorescence of the glass backing of the photographic plates

Emotional reactivity in infants with congenital heart defects: findings from a large case-cohort study in Norway

AIM: Advances in medical treatment in recent years have led to dramatically improved survival rates of children with severe congenital heart defects (CHD). However, very little is known about the psychological consequences for these children, particularly during and after the early period of invasive treatment. In this study, we investigated the extent to which the severity of the CHD affects the child's emotional reactivity at 6 months of age. METHOD: We linked prospective data from the Norwegian Mother and Child Cohort Study, conducted by the Norwegian Institute of Public Health with a nationwide medical CHD registry and identified 212 infants with CHD in a cohort of 61 299 infants. Mothers reported on their child's emotional reactivity at age 6 months by means of a standardized questionnaire. RESULTS: Infants with severe to moderate CHD had 60% higher odds for severe emotional reactivity (cut-off at the 85 percentile) compared with healthy infants, after controlling for important maternal and child confounders. CONCLUSION: Our study is the first to show elevated emotional reactivity in children with moderate to severe CHD, suggesting a need for special parental attention to soothe their distress. Follow-up studies will show whether this emotional reactivity is transient or an early marker of continuing emotional or behavioural problems

Protein engineering of a ubiquitin-variant inhibitor of APC/C identifies a cryptic K48 ubiquitin chain binding site.

Ubiquitin (Ub)-mediated proteolysis is a fundamental mechanism used by eukaryotic cells to maintain homeostasis and protein quality, and to control timing in biological processes. Two essential aspects of Ub regulation are conjugation through E1-E2-E3 enzymatic cascades and recognition by Ub-binding domains. An emerging theme in the Ub field is that these 2 properties are often amalgamated in conjugation enzymes. In addition to covalent thioester linkage to Ub's C terminus for Ub transfer reactions, conjugation enzymes often bind noncovalently and weakly to Ub at "exosites." However, identification of such sites is typically empirical and particularly challenging in large molecular machines. Here, studying the 1.2-MDa E3 ligase anaphase-promoting complex/cyclosome (APC/C), which controls cell division and many aspects of neurobiology, we discover a method for identifying unexpected Ub-binding sites. Using a panel of Ub variants (UbVs), we identify a protein-based inhibitor that blocks Ub ligation to APC/C substrates in vitro and ex vivo. Biochemistry, NMR, and cryo-electron microscopy (cryo-EM) structurally define the UbV interaction, explain its inhibitory activity through binding the surface on the APC2 subunit that recruits the E2 enzyme UBE2C, and ultimately reveal that this APC2 surface is also a Ub-binding exosite with preference for K48-linked chains. The results provide a tool for probing APC/C activity, have implications for the coordination of K48-linked Ub chain binding by APC/C with the multistep process of substrate polyubiquitylation, and demonstrate the power of UbV technology for identifying cryptic Ub-binding sites within large multiprotein complexes

Rough Fibrils Provide a Toughening Mechanism in Biological Fibers

Spider silk is a fascinating natural composite material. Its combination of strength and toughness is unrivalled in nature, and as a result, it has gained considerable interest from the medical, physics, and materials communities. Most of this attention has focused on the one to tens of nanometer scale: predominantly the primary (peptide sequences) and secondary (β sheets, helices, and amorphous domains) structure, with some insights into tertiary structure (the arrangement of these secondary structures) to describe the origins of the mechanical and biological performance. Starting with spider silk, and relating our findings to collagen fibrils, we describe toughening mechanisms at the hundreds of nanometer scale, namely, the fibril morphology and its consequences for mechanical behavior and the dissipation of energy. Under normal conditions, this morphology creates a nonslip fibril kinematics, restricting shearing between fibrils, yet allowing controlled local slipping under high shear stress, dissipating energy without bulk fracturing. This mechanism provides a relatively simple target for biomimicry and, thus, can potentially be used to increase fracture resistance in synthetic materials

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s) = 1.96 TeV

We present a measurement of the top quark pair production cross section in ppbar collisions at sqrt(s)=1.96 TeV using 318 pb^{-1} of data collected with the Collider Detector at Fermilab. We select ttbar decays into the final states e nu + jets and mu nu + jets, in which at least one b quark from the t-quark decays is identified using a secondary vertex-finding algorithm. Assuming a top quark mass of 178 GeV/c^2, we measure a cross section of 8.7 +-0.9 (stat) +1.1-0.9 (syst) pb. We also report the first observation of ttbar with significance greater than 5 sigma in the subsample in which both b quarks are identified, corresponding to a cross section of 10.1 +1.6-1.4(stat)+2.0-1.3 (syst) pb.Comment: Accepted for publication in Physics Review Letters, 7 page

Polarizations of J/psi and psi(2S) Mesons Produced in ppbar Collisions at 1.96 TeV

We have measured the polarizations of \jpsi and \psiprime mesons as functions of their transverse momentum \pt when they are produced promptly in the rapidity range $|y|<0.6$ with \pt \geq 5 \pgev. The analysis is performed using a data sample with an integrated luminosity of about 800 \ipb collected by the CDF II detector. For both vector mesons, we find that the polarizations become increasingly longitudinal as \pt increases from 5 to 30 \pgev. These results are compared to the predictions of nonrelativistic quantum chromodynamics and other contemporary models. The effective polarizations of \jpsi and \psiprime mesons from $B$-hadron decays are also reported.Comment: 8 pages, 7 figures, published in Physical Review Letter

Observation and Mass Measurement of the Baryon Ξb−\Xi^-_b

We report the observation and measurement of the mass of the bottom, strange baryon $\Xi^-_b$ through the decay chain $\Xi^-_b \to J/\psi \Xi^-$, where $J/\psi \to \mu^+ \mu^-$, $\Xi^- \to \Lambda \pi^-$, and $\Lambda \to p \pi^-$. Evidence for observation is based on a signal whose probability of arising from the estimated background is 6.6 x 10^{-15}, or 7.7 Gaussian standard deviations. The $\Xi^-_b$ mass is measured to be $5792.9\pm 2.5$ (stat.) $\pm 1.7$ (syst.) MeV/$c^2$.Comment: Minor text changes for the second version. Accepted by Phys. Rev. Let