Unchanged frequency and decreasing magnitude of outbursts from ice-dammed lakes in Alaska.

Glacial lakes can form and grow due to glacial retreat, and rapid lake drainage can produce destructive floods. Outburst flood compilations show a temporal increase in frequency; however, recent studies highlight the role of observational bias, creating uncertainty about current and future glacial-lake hazards. Here, we focus on the Alaska region, which generated a third of previously documented outbursts globally. Using multitemporal satellite imagery, we documented 1150 drainages from 106 ice-dammed lakes between 1985 and 2020. Documented events became more frequent over time, however, accounting for increasing image availability reveals no significant increase occurred. Most lakes decreased in area and volume, suggesting a reduction in regional flood hazard. Our satellite-based approach documented 60% more events in a 35-year period than had previously been documented over 100 years. This suggests that outburst floods have historically been underreported and warrants systematic study of other regions.

First Measurement of Hard Exclusive π

The polarized cross-section ratio σ_{LT^{'}}/σ_{0} from hard exclusive π^{-}Δ^{++} electroproduction off an unpolarized hydrogen target has been extracted based on beam-spin asymmetry measurements using a 10.2 GeV/10.6 GeV incident electron beam and the CLAS12 spectrometer at Jefferson Lab. The study, which provides the first observation of this channel in the deep-inelastic regime, focuses on very forward-pion kinematics in the valence regime, and photon virtualities ranging from 1.5 GeV^{2} up to 7 GeV^{2}. The reaction provides a novel access to the d-quark content of the nucleon and to p→Δ^{++} transition generalized parton distributions. A comparison to existing results for hard exclusive π^{+}n and π^{0}p electroproduction is provided, which shows a clear impact of the excitation mechanism, encoded in transition generalized parton distributions, on the asymmetry.

First Measurement of Λ Electroproduction off Nuclei in the Current and Target Fragmentation Regions.

We report results of Λ hyperon production in semi-inclusive deep-inelastic scattering off deuterium, carbon, iron, and lead targets obtained with the CLAS detector and the Continuous Electron Beam Accelerator Facility 5.014 GeV electron beam. These results represent the first measurements of the Λ multiplicity ratio and transverse momentum broadening as a function of the energy fraction (z) in the current and target fragmentation regions. The multiplicity ratio exhibits a strong suppression at high z and an enhancement at low z. The measured transverse momentum broadening is an order of magnitude greater than that seen for light mesons. This indicates that the propagating entity interacts very strongly with the nuclear medium, which suggests that propagation of diquark configurations in the nuclear medium takes place at least part of the time, even at high z. The trends of these results are qualitatively described by the Giessen Boltzmann-Uehling-Uhlenbeck transport model, particularly for the multiplicity ratios. These observations will potentially open a new era of studies of the structure of the nucleon as well as of strange baryons.

Determining the gluonic gravitational form factors of the proton.

The proton is one of the main building blocks of all visible matter in the Universe1. Among its intrinsic properties are its electric charge, mass and spin2. These properties emerge from the complex dynamics of its fundamental constituents-quarks and gluons-described by the theory of quantum chromodynamics3-5. The electric charge and spin of protons, which are shared among the quarks, have been investigated previously using electron scattering2. An example is the highly precise measurement of the electric charge radius of the proton6. By contrast, little is known about the inner mass density of the proton, which is dominated by the energy carried by gluons. Gluons are hard to access using electron scattering because they do not carry an electromagnetic charge. Here we investigated the gravitational density of gluons using a small colour dipole, through the threshold photoproduction of the J/ψ particle. We determined the gluonic gravitational form factors of the proton7,8 from our measurement. We used a variety of models9-11 and determined, in all cases, a mass radius that is notably smaller than the electric charge radius. In some, but not all cases, depending on the model, the determined radius agrees well with first-principle predictions from lattice quantum chromodynamics12. This work paves the way for a deeper understanding of the salient role of gluons in providing gravitational mass to visible matter.

Observation of Correlations between Spin and Transverse Momenta in Back-to-Back Dihadron Production at CLAS12.

We report the first measurements of deep inelastic scattering spin-dependent azimuthal asymmetries in back-to-back dihadron electroproduction in the deep inelastic scattering process. In this reaction, two hadrons are produced in opposite hemispheres along the z axis in the virtual photon-target nucleon center-of-mass frame, with the first hadron produced in the current-fragmentation region and the second in the target-fragmentation region. The data were taken with longitudinally polarized electron beams of 10.2 and 10.6 GeV incident on an unpolarized liquid-hydrogen target using the CLAS12 spectrometer at Jefferson Lab. Observed nonzero sinΔϕ modulations in ep→e^{'}pπ^{+}X events, where Δϕ is the difference of the azimuthal angles of the proton and pion in the virtual photon and target nucleon center-of-mass frame, indicate that correlations between the spin and transverse momenta of hadrons produced in the target- and current-fragmentation regions may be significant. The measured beam-spin asymmetries provide a first access in dihadron production to a previously unexplored leading-twist spin- and transverse-momentum-dependent fracture function. The fracture functions describe the hadronization of the target remnant after the hard scattering of a virtual photon off a quark in the target particle and provide a new avenue for studying nucleonic structure and hadronization.

Observation of Azimuth-Dependent Suppression of Hadron Pairs in Electron Scattering off Nuclei.

We present the first measurement of dihadron angular correlations in electron-nucleus scattering. The data were taken with the CLAS detector and a 5.0 GeV electron beam incident on deuterium, carbon, iron, and lead targets. Relative to deuterium, the nuclear yields of charged-pion pairs show a strong suppression for azimuthally opposite pairs, no suppression for azimuthally nearby pairs, and an enhancement of pairs with large invariant mass. These effects grow with increased nuclear size. The data are qualitatively described by the gibuu model, which suggests that hadrons form near the nuclear surface and undergo multiple scattering in nuclei.These results show that angular correlation studies can open a new way to elucidate how hadrons form and interact inside nuclei.

Measurement of the Nucleon F_{2}

The ratio of the nucleon F_{2} structure functions, F_{2}^{n}/F_{2}^{p}, is determined by the MARATHON experiment from measurements of deep inelastic scattering of electrons from ^{3}H and ^{3}He nuclei. The experiment was performed in the Hall A Facility of Jefferson Lab using two high-resolution spectrometers for electron detection, and a cryogenic target system which included a low-activity tritium cell. The data analysis used a novel technique exploiting the mirror symmetry of the two nuclei, which essentially eliminates many theoretical uncertainties in the extraction of the ratio. The results, which cover the Bjorken scaling variable range 0.19

Ruling out Color Transparency in Quasielastic

Quasielastic ^{12}C(e,e^{'}p) scattering was measured at spacelike 4-momentum transfer squared Q^{2}=8, 9.4, 11.4, and 14.2 (GeV/c)^{2}, the highest ever achieved to date. Nuclear transparency for this reaction was extracted by comparing the measured yield to that expected from a plane-wave impulse approximation calculation without any final state interactions. The measured transparency was consistent with no Q^{2} dependence, up to proton momenta of 8.5 GeV/c, ruling out the quantum chromodynamics effect of color transparency at the measured Q^{2} scales in exclusive (e,e^{'}p) reactions. These results impose strict constraints on models of color transparency for protons.

Improved Λp Elastic Scattering Cross Sections between 0.9 and 2.0 GeV/c as a Main Ingredient of the Neutron Star Equation of State.

Strange matter is believed to exist in the cores of neutron stars based on simple kinematics. If this is true, then hyperon-nucleon interactions will play a significant part in the neutron star equation of state. Yet, compared to other elastic scattering processes, there is very little data on Λ-N scattering. This experiment utilized the CEBAF Large Acceptance Spectrometer (CLAS) detector to study the Λp→Λp elastic scattering cross section in the incident Λ momentum range 0.9-2.0 GeV/c. These are the first data on this reaction since the 1970s. The new cross sections have significantly better accuracy and precision than the existing world data, and the techniques developed here can also be used in future experiments.

First Measurement of Timelike Compton Scattering.

We present the first measurement of the timelike Compton scattering process, γp→p^{'}γ^{*}(γ^{*}→e^{+}e^{-}), obtained with the CLAS12 detector at Jefferson Lab. The photon beam polarization and the decay lepton angular asymmetries are reported in the range of timelike photon virtualities 2.25

Probing Few-Body Nuclear Dynamics via

We report the first measurement of the (e,e^{'}p) three-body breakup reaction cross sections in helium-3 (^{3}He) and tritium (^{3}H) at large momentum transfer [⟨Q^{2}⟩≈1.9 (GeV/c)^{2}] and x_{B}>1 kinematics, where the cross section should be sensitive to quasielastic (QE) scattering from single nucleons. The data cover missing momenta 40≤p_{miss}≤500 MeV/c that, in the QE limit with no rescattering, equals the initial momentum of the probed nucleon. The measured cross sections are compared with state-of-the-art ab initio calculations. Overall good agreement, within ±20%, is observed between data and calculations for the full p_{miss} range for ^{3}H and for 100≤p_{miss}≤350 MeV/c for ^{3}He. Including the effects of rescattering of the outgoing nucleon improves agreement with the data at p_{miss}>250 MeV/c and suggests contributions from charge-exchange (SCX) rescattering. The isoscalar sum of ^{3}He plus ^{3}H, which is largely insensitive to SCX, is described by calculations to within the accuracy of the data over the entire p_{miss} range. This validates current models of the ground state of the three-nucleon system up to very high initial nucleon momenta of 500 MeV/c.

Probing the Deuteron at Very Large Internal Momenta.

We measure ^{2}H(e,e^{'}p)n cross sections at 4-momentum transfers of Q^{2}=4.5±0.5 (GeV/c)^{2} over a range of neutron recoil momenta p_{r}, reaching up to ∼1.0 GeV/c. We obtain data at fixed neutron recoil angles θ_{nq}=35°, 45°, and 75° with respect to the 3-momentum transfer q[over →]. The new data agree well with previous data, which reached p_{r}∼500 MeV/c. At θ_{nq}=35° and 45°, final state interactions, meson exchange currents, and isobar currents are suppressed and the plane wave impulse approximation provides the dominant cross section contribution. We compare the new data to recent theoretical calculations, where we observe a significant discrepancy for recoil momenta p_{r}>700 MeV/c.

Revealing Color Forces with Transverse Polarized Electron Scattering.

The Spin Asymmetries of the Nucleon Experiment measured two double spin asymmetries using a polarized proton target and polarized electron beam at two beam energies, 4.7 and 5.9 GeV. A large-acceptance open-configuration detector package identified scattered electrons at 40° and covered a wide range in Bjorken x (0.3

Mass spectrometry detection of basic drugs in fast chiral analyses with vancomycin stationary phases / 药物分析学报

Current trends in chiral analysis of pharmaceutical drugs are focused on faster separations and higher separation efficiencies. Core-shell or superficially porous particles (SPP) based chiral stationary phases (CSPs) provide reduced analysis times while maintaining high column efficiencies and sensitivity. In this study, mobile phase conditions suitable for chiral analyses with electrospray ionization LC-MS were systematically investigated using vancomycin as a representative CSP. The performance of a 2.7 μm SPP based vancomycin CSP (SPP-V) 10 cm × 0.21 cm column was compared to that of a corresponding 5 μm fully porous particles based analogue column. The results demonstrated that the SPP-V column provides higher efficiencies, 2–5 time greater sensitivity and shorter analysis time for a set of 22 basic pharma-ceutical drugs. The SPP-V was successfully applied for the analysis of the degradation products of racemic citalopram whose enantiomers could be selectively identified by MS.

Late Pregnancy is a Critical Period for Changes in Phosphorylated Mitogen-Activated Protein Kinase/Extracellular Signal-Regulated Kinase 1/2 in Oxytocin Neurones.

The physiological demands of parturition and lactation lead to the increased pulsatile release of oxytocin (OT) into the circulation from the neurohypophysial axons of OT neurones in the supraoptic (SON) and paraventricular (PVN) nuclei. These states of increased OT release are accompanied by a significant plasticity in magnocellular OT neurones and their synaptic connections, and many of these changes require activation of a central OT receptor. The mitogen-activated protein kinase/extracellular signal-regulated kinase pathway (MAPK/ERK) is assumed to be up-regulated in the PVN during lactation, and many of the effects of OT in peripheral and brain tissue are mediated through a MAPK/ERK pathway. The present study investigated whether this pathway is altered in the SON and PVN during late pregnancy [embryonic day (E)20-21], which is a critical period for OT plasticity induction, and for lactation, when plastic changes are sustained. Based on immunoreactivity for phosphorylated ERK1/2 (pERK1/2), the results suggest an enhanced activation of MAPK/ERK pathway in OT neurones specifically during late pregnancy in both the SON and PVN. Although immunoblots from the SON confirm this pregnancy-associated up-regulation in late pregnancy, they also suggest enhancement into lactation as well. Together, the results suggest an important role for the MAPK/ERK pathway during reproductive changes in the SON and PVN.

Screening primary racemic amines for enantioseparation by derivatized polysaccharide and cyclofructan columns☆ / 药物分析学报

It is a challenge to separate the enantiomers of native chiral amines prone to deleterious silanol interactions. A set of 39 underivatized chiral primary amines was screened for enantiomeric separation. Seven recently introduced commercial chiral columns were tested. They included six polysaccharide based chiral stationary phases (CSP) with bonded derivatives, ChiralPak? IA, IB, IC, ID, IE and IF columns and a cyclofructan derivatized CSP, Larihc? CF6-P column. Both the normal phase (NP) mode with heptane/alcohol mobile phases and the polar organic (PO) mode with acetonitrile/alcohol were evaluated. It was found that the cyclofructan based CSP demonstrated the highest success rate in separating primary amines in the PO mode with only one chiral amine not resolved. It is shown that, when screening the columns, there is no standard optimal condition;an excellent mobile phase composition for one column may be poorly suited to another one. Although butylamine was a good mobile phase additive for the polysaccharide columns in both PO and NP modes, it was detrimental to the enantio-recognition capability of the cyclofructan column. Triethylamine was the appropriate silanol screening agent for this latter column.

Wavelet-based intensity analysis of the mechanomyograph and electromyograph during the H-reflex.

PURPOSE: The relationship between mechanomyography (MMG) and electromyography (sEMG) during electrically evoked muscle contraction was examined using the von Tscharner "intensity analysis," which describes the power of a non-stationary signal as a function of both frequency and time. METHOD: Data for 8 college-aged participants (3 males; 5 females) with measurable H-reflexes were analyzed. Recruitment curves for H-reflex (H), M-wave (M) using sEMG, and peak-to-peak MMG (MMGp-p) were elicited through incremental tibial nerve stimulation. The maximum peak-to-peak values for H and M for each sample were summed (HM); and maximum intensity values were measured for MMG, H, and M following the intensity analysis and computation of total intensity (MMGCvT, HCvT, MCvT). HCvT and MCvT were subsequently added together (HMCvT) for comparisons. RESULTS: Correlations of HM:MMGp-p, HM:MMGCvT, HMCvT:MMGCvT, HMCvT:MMGp-p, were low (r = 0.34, 0.33, 0.09, and 0.12, respectively, p < 0.001); and correlations of HM:HMCvT, MMGCvT:MMGp-p, were moderate-to-high (r = 0.69 and 0.97, respectively, p < 0.001). Correlations for individuals ranged from 0.61 to 0.99 across comparisons. The time at which maximal intensities occurred reflected the transition from a predominant H-reflex to the onset of the M-wave and declining lag times were noted with increasing intensity. CONCLUSIONS: The intensity analysis provides insight into the frequency characteristics of the H-reflex and M-wave not seen in traditional analysis of the H-reflex. The intensity analysis may be a useful tool in studying individual variations and changes in the contraction velocities of skeletal muscle.

Precision measurement of the neutron twist-3 matrix element d(2)(n): probing color forces.

Double-spin asymmetries and absolute cross sections were measured at large Bjorken x (0.25≤x≤0.90), in both the deep-inelastic and resonance regions, by scattering longitudinally polarized electrons at beam energies of 4.7 and 5.9 GeV from a transversely and longitudinally polarized (3)He target. In this dedicated experiment, the spin structure function g(2)((3)He) was determined with precision at large x, and the neutron twist-3 matrix element d(2)(n) was measured at ⟨Q(2)⟩ of 3.21 and 4.32 GeV(2)/c(2), with an absolute precision of about 10(-5). Our results are found to be in agreement with lattice QCD calculations and resolve the disagreement found with previous data at ⟨Q(2)⟩=5 GeV(2)/c(2). Combining d(2)(n) and a newly extracted twist-4 matrix element f(2)(n), the average neutron color electric and magnetic forces were extracted and found to be of opposite sign and about 30 MeV/fm in magnitude.