The near-Earth asteroid 162173 Ryugu, the target of the Hayabusa2 sample-return mission, is thought to be a primitive carbonaceous object. We report reflectance spectra of Ryugu's surface acquired ...with the Near-Infrared Spectrometer (NIRS3) on Hayabusa2, to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micrometers was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, which is consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.
The PHENIX experiment measured the centrality dependence of two-pion
Bose-Einstein correlation functions in $\sqrt{s_{_{NN}}}=200$~GeV Au$+$Au
collisions at the Relativistic Heavy Ion Collider at ...Brookhaven National
Laboratory. The data are well represented by L\'evy-stable source
distributions. The extracted source parameters are the correlation-strength
parameter $\lambda$, the L\'evy index of stability $\alpha$, and the
L\'evy-scale parameter $R$ as a function of transverse mass $m_T$ and
centrality. The $\lambda(m_T)$ parameter is constant at larger values of $m_T$,
but decreases as $m_T$ decreases. The L\'evy scale parameter $R(m_T)$ decreases
with $m_T$ and exhibits proportionality to the length scale of the nuclear
overlap region. The L\'evy exponent $\alpha(m_T)$ is independent of $m_T$
within uncertainties in each investigated centrality bin, but shows a clear
centrality dependence. At all centralities, the L\'evy exponent $\alpha$ is
significantly different from that of Gaussian ($\alpha=2$) or Cauchy
($\alpha=1$) source distributions. Comparisons to the predictions of
Monte-Carlo simulations of resonance-decay chains show that in all but the most
peripheral centrality class (50%-60%), the obtained results are inconsistent
with the measurements, unless a significant reduction of the in-medium mass of
the $\eta'$ meson is included. In each centrality class, the best value of the
in-medium $\eta'$ mass is compared to the mass of the $\eta$ meson, as well as
to several theoretical predictions that consider restoration of $U_A(1)$
symmetry in hot hadronic matter.
Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou, the masses of 82Zr and 84Nb were measured for the first time with an uncertainty of ∼10 keV, and the masses of ...79Y, 81Zr, and 83Nb were re-determined with a higher precision. The latter are significantly less bound than their literature values. Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart. Our results do not support the predicted island of pronounced low α separation energies for neutron-deficient Mo and Tc isotopes, making the formation of Zr–Nb cycle in the rp-process unlikely. The new proton separation energy of 83Nb was determined to be 490(400) keV smaller than that in the Atomic Mass Evaluation 2012. This partly removes the overproduction of the p-nucleus 84Sr relative to the neutron-deficient molybdenum isotopes in the previous νp-process simulations.
Abstract
A novel isochronous mass spectrometry, termed as
$$B\rho $$
B
ρ
-defined IMS, has been established at the experimental cooler-storage ring CSRe in Lanzhou. Its potential has been studied ...through high precision mass measurements of
$$^{58}$$
58
Ni projectile fragments. Two time-of-flight detectors were installed in one of the straight sections of CSRe, thus enabling simultaneous measurements of the velocity and the revolution time of each stored short-lived ion. This allows for calculating the magnetic rigidity
$$B\rho $$
B
ρ
and the orbit length
C
of each ion. The accurate
$$B\rho (C)$$
B
ρ
(
C
)
function has been constructed, which is a universal calibration curve used to deduce the masses of the stored nuclides. The sensitivity to single stored ions, fast measurement time, and background-free characteristics of the method are ideally suited to address nuclides with very short lifetimes and smallest production yields. In the limiting case of just a single particle, the achieved mass resolving power allows one to determine its mass-over-charge ratio
m
/
q
with a remarkable precision of merely
$$\sim 5$$
∼
5
keV. Masses of
$$T_z=-3/2$$
T
z
=
-
3
/
2
fp
-shell nuclides are re-determined with high accuracy, and the validity of the isospin multiplet mass equation is tested up to the heaviest isospin quartet with
$$A=55$$
A
=
55
. The new masses are also used to investigate the mirror symmetry of empirical residual proton-neutron interactions.
We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element /Vub/, based on 253 fb(-1) of data collected by the Belle detector at the KEKB e+ e- asymmetric collider. Events are tagged by ...fully reconstructing one of the B mesons, produced in pairs from Gamma(4S). The signal for b --> u semileptonic decay is distinguished from the b --> c background using the hadronic mass Mx, the leptonic invariant mass squared q2 and the variable P+ triple bond Ex - /px/. The results are obtained for events with p(l)* > or = 1 GeV/c, in three kinematic regions (1) Mx < 1.7 GeV/c2, (2) Mx < 1.7 GeV/c2 combined with q2 > 8 GeV2/c2, and by (3) P+ < 0.66 GeV/c. The matrix element /Vub/ is found to be (4.09 +/- 0.19 +/- 0.20(+0.14) -0.15 +/- 0.18) x 10(-3), where the errors are statistical, systematic including Monte Carlo modeling, theoretical, and from shape function parameter determination, respectively.
Memories are encoded within sparsely distributed neuronal ensembles. However, the defining cellular properties of neurons within a memory trace remain incompletely understood. Using a ...fluorescence-based Arc reporter, we were able to visually identify the distinct subset of lateral amygdala (LA) neurons activated during auditory fear conditioning. We found that Arc-expressing neurons have enhanced intrinsic excitability and are preferentially recruited into newly encoded memory traces. Furthermore, synaptic potentiation of thalamic inputs to the LA during fear conditioning is learning-specific, postsynaptically mediated and highly localized to Arc-expressing neurons. Taken together, our findings validate the immediate-early gene Arc as a molecular marker for the LA neuronal ensemble recruited during fear learning. Moreover, these results establish a model of fear memory formation in which intrinsic excitability determines neuronal selection, whereas learning-related encoding is governed by synaptic plasticity.
Abstract
As accelerators and electron microscopes become more advanced, high-performance photocathodes are required. In particular, Cesium potassium antimonide (CsK
2
Sb) photocathode is of interest ...because of its low emittance, excitability in visible light, and high quantum efficiency (QE). The challenge is its high susceptibility to environment that lead to low operating vacuum pressure and short lifetime/low extraction charge. To resolve these issues, it is necessary to understand the molecular structure of the cathode and its degradation mechanism. In this study, we transported CsK
2
Sb photocathode to a beamline of synchrotron radiation facility using a vacuum transport system for molecular structure analysis. Specifically, the cathode was deposited in an evaporation system at Nagoya University. We transported it to Aichi Synchrotron Radiation Center (Aichi SR) located 15 km away, and analyzed it in the depth direction by X-ray photoelectron spectroscopy (XPS) at BL7U. Based on the results, we quantitatively evaluated the composition ratios and stoichiometry of the cathode elements (Sb, K, Cs). A Cs ex-cess state of surface was observed at the surface, and it is consistent with previous studies. The intended atomic structure of CsK
2
Sb was formed only at a few nanometres of the surface on the Mo substrate. On the other hand, the CsK
2
Sb cathode structure on the graphene substrate was preserved further in the depth direction.
Isochronous mass spectrometry has been applied to neutron-deficient Ni-58 projectile fragments at the HIRFL-CSR facility in Lanzhou, China. Masses of a series of short-lived T-z = -3/2 nuclides ...including Ti-41, Cr-45, Fe-49, and Ni-53 have been measured with a precision of 20-40 keV. The new data enable us to test for the first time the isobaric multiplet mass equation (IMME) in f p-shell nuclei. We observe that the IMME is inconsistent with the generally accepted quadratic form for the A = 53, T = 3/2 quartet. We perform full space shell model calculations and compare them with the new experimental results.
PDF
