459 research outputs found
A CLASSIFICATION OF THE MURINE LEUKEMIA VIRUSES : NEUTRALIZATION OF PSEUDOTYPES OF FRIEND SPLEEN FOCUS-FORMING VIRUS BY TYPE-SPECIFIC MURINE ANTISERA
Coinfection of neonatal BALB/c mice with helper-dependent Friend spleen focus-forming virus (SFFV), as contained in the Friend virus (FV) complex, and antigenically distinct Moloney leukemia virus (MolLV) resulted in the recovery of a MolLV pseudotype of SFFV, abbreviated SFFV(MolLV). The antigenic alteration of SFFV was observed by following its neutralization kinetics in vitro by specific Friend or Moloney typing antiserum. Effective pseudotype production was accomplished only when N-tropic LLV-F (the natural helper virus in the FV complex) was inhibited in B-type mice coinfected with an NB-tropic MolLV or other murine leukemia virus (MuLV) preparation. SFFV pseudotypes could not be prepared by using murine viruses other than leukemia viruses. SFFV prepared after two serial passages in the presence of MolLV was effectively neutralized by Moloney antiserum, but not by Friend typing antiserum; therefore, the envelope of the pseudotype virus, SFFV(MolLV), is homogeneous. Pseudotype virus was antigenically stable in the absence of continued mixed infection of BALB/c mice with SFFV(MolLV) and MolLV. However, SFFV(MolLV) was easily converted back to the LLV-F type after only one passage in BALB/c mice coinfected with NB-tropic LLV-F. The antigenic interconversion between LLV-F and MolLV types demonstrated that SFFV is defective with respect to the expression of neutralizable envelope antigens. Analysis of the neutralizable envelope antigens of nine SFFV(MuLV) pseudotypes by a panel of seven typing antisera made possible a "type-specific" SFFV(MuLV) envelope classification. Two major categories have been identified which correspond to the Gross (G) and Friend-Moloney-Rauscher (FMR) subgroups. Further, the FMR subgroup was divided into four types on the basis of distinct neutralization patterns. These results indicated that the specificity observed by cytotoxic G vs. FMR antisera is different from that observed by neutralization kinetics. We therefore suggest that the specific antigens revealed by virus neutralization tests be referred to as type specific
Seconds-scale coherence in a tweezer-array optical clock
Optical clocks based on atoms and ions achieve exceptional precision and
accuracy, with applications to relativistic geodesy, tests of relativity, and
searches for dark matter. Achieving such performance requires balancing
competing desirable features, including a high particle number, isolation of
atoms from collisions, insensitivity to motional effects, and high duty-cycle
operation. Here we demonstrate a new platform based on arrays of ultracold
strontium atoms confined within optical tweezers that realizes a novel
combination of these features by providing a scalable platform for isolated
atoms that can be interrogated multiple times. With this tweezer-array clock,
we achieve greater than 3 second coherence times and record duty cycles up to
96%, as well as stability commensurate with leading platforms. By using optical
tweezer arrays --- a proven platform for the controlled creation of
entanglement through microscopic control --- this work further promises a new
path toward combining entanglement enhanced sensitivities with the most precise
optical clock transitions
Poster 194: Biomechanical Analysis of a Novel Clinical Measure of Reaction Time
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147091/1/pmr2s188a.pd
Harmonic Generation from Relativistic Plasma Surfaces in Ultra-Steep Plasma Density Gradients
Harmonic generation in the limit of ultra-steep density gradients is studied
experimentally. Observations demonstrate that while the efficient generation of
high order harmonics from relativistic surfaces requires steep plasma density
scale-lengths () the absolute efficiency of the harmonics
declines for the steepest plasma density scale-length , thus
demonstrating that near-steplike density gradients can be achieved for
interactions using high-contrast high-intensity laser pulses. Absolute photon
yields are obtained using a calibrated detection system. The efficiency of
harmonics reflected from the laser driven plasma surface via the Relativistic
Oscillating Mirror (ROM) was estimated to be in the range of 10^{-4} - 10^{-6}
of the laser pulse energy for photon energies ranging from 20-40 eV, with the
best results being obtained for an intermediate density scale-length
Poster 118 Is a Clinical Measure of Upper Limb Reaction Time Predictive of Lower Limb Neuromuscular Function?
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147067/1/pmr2s209b.pd
Blood Pressure and Global Risk Assessment in a Swedish Population
This study investigated the association between SCORE and the 2007 ESH-ESC blood pressure categories and explored achievements of blood pressure goals considering global risk. In 2001–2005, a random sample of inhabitants aged 30–74 years in southwestern Sweden was invited to a survey of cardiovascular risk factors. The study enrolled 2816 participants (participation rate 76%). Blood pressure was categorized according to the 2007 ESH-ESC guidelines. Global risk of 10-year CVD death was estimated using the Swedish SCORE chart also accounting for additional risk from diabetes (SCORE-DM). SCORE-DM increased in both sexes from optimal blood pressure to manifest hypertension but did not differ between the normal blood pressure categories. However, SCORE-DM became significantly higher among those with temporarily high blood pressure (men 3.3 SD (1.7), women 1.1 (1.8)) and hypertension (3.6 (2.0), 2.0 (2.0)), compared to optimal blood pressure (1.6 (2.9), 0.6 (1.9)). In the presence of both hypertension and diabetes, high-risk subjects dominated (men 76%, women 61%), and correspondingly a major proportion of patients with known hypertension were at high risk at a blood pressure ≥160/100 mm Hg. These findings have strong implications on blood pressure evaluation in clinical practice and support the use of SCORE to evaluate global risk
Experimental Observation of Attosecond Control over Relativistic Electron Bunches with Two-Colour Fields
A tweezer clock with half-minute atomic coherence at optical frequencies and high relative stability
The preparation of large, low-entropy, highly coherent ensembles of identical
quantum systems is foundational for many studies in quantum metrology,
simulation, and information. Here, we realize these features by leveraging the
favorable properties of tweezer-trapped alkaline-earth atoms while introducing
a new, hybrid approach to tailoring optical potentials that balances
scalability, high-fidelity state preparation, site-resolved readout, and
preservation of atomic coherence. With this approach, we achieve trapping and
optical clock excited-state lifetimes exceeding seconds in ensembles of
approximately atoms. This leads to half-minute-scale atomic coherence
on an optical clock transition, corresponding to quality factors well in excess
of . These coherence times and atom numbers reduce the effect of
quantum projection noise to a level that is on par with leading atomic systems,
yielding a relative fractional frequency stability of
for synchronous clock comparisons
between sub-ensembles within the tweezer array. When further combined with the
microscopic control and readout available in this system, these results pave
the way towards long-lived engineered entanglement on an optical clock
transition in tailored atom arrays.Comment: 11 pages, 5 figures (main text); 17 pages, 7 figures (supplemental
materials
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