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At least 451 records · Page 25

Thiol post-translational modifications modulate allosteric regulation of the OpcA–G6PDH complex through conformational gate control

In cyanobacteria, the redox-sensitive protein OpcA acts as a metabolic switch for G6PDH, enabling rapid adjustment of reducing power generation from glycogen catabolism and thereby precisely regulating carbon flux between anabolic and catabolic pathways. Although redox-sensitive cysteines in OpcA are known to regulate G6PDH, the mechanisms by which redox post-translational modifications (PTMs) on OpcA control G6PDH structure and activity remain unclear. Here, we combine computational modeling with experimental redox proteomics in Synechococcus elongatus PCC 7942 to dissect this mechanism. Experimentally, redox proteome analysis revealed differential redox PTM patterns, particularly on cysteines within the G6PDH-binding site of OpcA. These environmentally sensitive PTM changes at the interface suggest that thiol modifications in this region form a key regulatory node. More broadly, redox proteomics identified site-specific cysteine modifications under light/dark transitions and circadian cycling, linking distinct redox regimes to discrete PTM states. We employed PTM-Psi simulations to show that thiol PTMs near the OpcA–G6PDH interface are critical for allosteric regulation of G6PDH. The thiol PTMs on OpcA affect a putative gate region in G6PDH for substrate ingress and product egress as well as key hydrogen-bond networks within the active site. We infer that PTMs on OpcA tune the conformational landscapes of individual G6PDH subunits toward functionally relevant configurations according to environmental gradients, biasing the enzyme toward catalytically favorable states. Together, our results reveal a molecular mechanism in which thiol PTMs on OpcA modulate G6PDH structure and function through PTM-induced reorganization of conformational dynamics and allosteric communication. These findings demonstrate that PTM-level regulation provides a critical control layer from genotypes to phenotypes that enables cyanobacteria to rapidly adapt to environmental fluctuations through precise metabolic fine-tuning.

Allosteric regulation↗

Computation of Sensitivity Derivatives of Navier-Stokes Equations using Complex Variables

Accurate computation of sensitivity derivatives is becoming an important item in Computational Fluid Dynamics (CFD) because of recent emphasis on using nonlinear CFD methods in aerodynamic design, optimization, stability and control related problems. Several techniques are available to compute gradients or sensitivity derivatives of desired flow quantities or cost functions with respect to selected independent (design) variables. Perhaps the most common and oldest method is to use straightforward finite-differences for the evaluation of sensitivity derivatives. Although very simple, this method is prone to errors associated with choice of step sizes and can be cumbersome for geometric variables. The cost per design variable for computing sensitivity derivatives with central differencing is at least equal to the cost of three full analyses, but is usually much larger in practice due to difficulty in choosing step sizes. Another approach gaining popularity is the use of Automatic Differentiation software (such as ADIFOR) to process the source code, which in turn can be used to evaluate the sensitivity derivatives of preselected functions with respect to chosen design variables. In principle, this approach is also very straightforward and quite promising. The main drawback is the large memory requirement because memory use increases linearly with the number of design variables. ADIFOR software can also be cumber-some for large CFD codes and has not yet reached a full maturity level for production codes, especially in parallel computing environments.

Vatsa, Veer N.↗

Stability of partially lined combustors with distributed combustion

An integral method for theoretical evaluation of the stability of confined flows with mass sources is presented. This method is applied to evaluate the effect of partial length acoustic liners on liquid propellant combustors with distributed combustion sources. The combustor is modeled as a right circular cylinder terminated by a multiorifice (constant Mach number) nozzle. The spatial spread of combustion in the chamber is represented by an arbitrary number of pressure sensitive planar mass sources. On the cylindrical periphery of the chamber is an acoustic absorber of arbitrary length, position, and damping capability. Integral equations are developed from the partial differential equations describing the nonsteady flow and are solved iteratively. Results are given in terms of linear neutral stability plots using a pressure sensitive combustion response. Calculations indicate that increasing the axial spread of combustion increases the stability of the combustor and the effectiveness of the absorber. The most effective linear placement appears at the location of greatest combustion concentration.

Baer, M. R.↗

Gravitropic curvature of maize roots is not preceded by rootcap asymmetry

We tested whether the first response to gravistimulation is an asymmetry in the root tip that results from differential growth of the rootcap itself. The displacement of markers on the rootcap surface of maize (Zea mays L. cv. Merit) roots was quantified from videotaped images using customized software. The method was sensitive enough to detect marker displacements down to 15 microns and root curvature as early as 8 min after gravistimulation. No differential growth of the upper and lower sides of the cap occurred before or during root curvature. Fewer than a third of all gravistimulated roots developed an asymmetrical outline of the root tip after curvature had started, and this asymmetry did not occur in the rootcap itself. Our data support the view that the regions of gravitropic sensing and curvature are spatially separate during all phases of gravitropism in maize roots.

NASA Program Space Biology↗

Pulsed Lidar for Measurement of C02 Concentrations for the ASCENDS Mission - Update

We have been developing a laser-based sounding technique for the remote measurement of the tropospheric CO2 concentrations from orbit for NASA is ASCENDS mission. The mission's goals are to provide measurements of tropospheric CO2 abundance with global-coverage, a few hundred km spatial and monthly temporal resolution. These are needed to better understand CO2 fluxes and the processes that regulate CO2 storage by the land and oceans. For the lIP, we are developing and demonstrating the lidar techniques and key lidar technology that will permit measurements of the CO2 column abundance in the lower troposphere from aircraft. Our final goal is to demonstrate the key capabilities needed for a space lidar and mission approach for the ASCENDS mission. We use a pulsed lidar technique, which is much less sensitive to errors from cloud and atmospheric scattering and to noise from solar background. It allows continuous measurements of CO2 mixing ratio in the lower troposphere during day and night. Our approach uses the 1570nm CO2 band and a two-wavelength laser absorption spectrometer, which continuously measures at nadir from a circular polar orbit. It directs the narrow co-aligned laser beams from the instrument's lasers toward nadir, and measures the energy of the laser echoes reflected from land and water surfaces. It uses a pair of tunable laser transmitters, which allowing measurement of the extinction from a single selected CO2 absorption line in the 1570 nm band and from a line pair in the Oxygen A-band near 765 nm. These regions have temperature insensitive absorption lines are free from interference from other gases. The lasers pulse at 10KHz, use tunable diode seed lasers followed by laser amplifiers, and have MHz spectral widths. During the measurement the lasers are stepped across the selected lines at a kHz rate. The receiver uses a 1-m class telescope and photon sensitive detectors and measures the background light and energies of the laser echoes from the surface. The extinction and column densities for the CO2 and O2 gases are estimated from the ratio of the on and off line echo pulse energies via the integrated path differential absorption (IPDA) technique. Our technique exploits the atmospheric pressure broadening of the lines to weight the measurement sensitivity to the atmospheric column below 5 km. Pulsed laser signals, time gated receiver are used to isolate the surface laser echo signals and to exclude photons scattered from clouds and aerosols. We have successfully demonstrated many key aspects of the approach and lidar technology in the laboratory. We have demonstrated CO2 column measurements in airborne flights during the summers of 2009 and 2010. These included measurements from 3-l3 km altitudes made over a variety of surfaces and through thin and broken clouds. We demonstrated initial airborne measurements of O2 column density to 10 km altitudes during the summer 2010 flights. More details approach, key technologies, and demonstration measurements will be given in the presentation.

Abshire, James↗

Nd-142/Nd-144 in bulk planetary reservoirs, the problem of incomplete mixing of interstellar components and significance of very high precision Nd-145/Nd-144 measurements

Apart from the challenge of very high precision Nd-142/Nd-144 ratio measurement, accurate applications of the coupled Sm-(146,147)-Nd-(142,143) systematics in planetary differentiation studies require very precise knowledge of the present-day (post-Sm-146 decay) Nd-142/Nd-144 ratios of bulk planetary objects (BP). The coupled systematics yield model ages for the time of formation of Sm/Nd-fractionated reservoirs by differentiation of Sm/Nd-unfractionated bulk planetary reservoirs. Estimates of (Nd-142/Nd-144)(sub BP) and (Nd-143/Nd-144)(sub BP) therefore provide the critical baseline relative to which these model ages are referenced. In the Sm-147-Nd-143 systematics, Nd-143/Nd-144 variations are mostly large; therefore, small variations in initial Nd-143/Nd-144 ratios generally can be ignored. However, in the case of Sm-146-Nd-142, the range of Nd-142/Nd-144 divergence for differentiated planetary reservoirs is much smaller. Consequently Sm-(146,147)-Nd-(142,143) model ages are sensitive to small variations in bulk planetary Nd-142/Nd-144 (both present-day and initial). One major unanswered question is whether or not Nd shelf standards (CIT Nd beta/Ames metal, La Jolla, NASA-JSC/Ames metal) have Nd-142/Nd-144 identical to the bulk Earth or otherwise might record some degree of radiogenic evolution in an early-fractionated reservoir. Our discussions of earth Earth differentiation based on Nd-142/Nd-144 in Isua and Acasta samples have employed a working assumption: (Nd-142/Nd-144)(sub Nd beta) = (Nd-142/Nd-144)(sub Bulk Earth). This requires experimental justification and is apparently contradicted by chondrite Nd-142/Nd-144 measurements, which have been interpreted to indicate: (Nd-142/Nd-144)(sub JSC/Ames metal) = ((Nd-142/Nd-144)(sub CHUR) = 35 plus or minus 8 ppm). At present, interpretations of the early Earth and Moon hinge largely on this issue. Because Ba in bulk chondrite samples exhibit similar magnitude nuclear anomalies, attributable to incomplete mixing of interstellar components, a critical question is whether or not nuclear effects are also present in Nd-142/Nd-144, both in bulk chondrites and between planetary objects.

Harper, C. L., Jr.↗

Development of the multi-purpose Cologne Compact Differential Plunger (CoCoDiff) for the measurement of nuclear level lifetimes with the Recoil Distance Doppler-shift method

Here, a new 3-foil plunger device, the Cologne Compact Differential (CoCoDiff) plunger has been built and commissioned. Due to its compact size, it can be used together with many different spectrometers and auxiliary detectors. As a commissioning experiment, level lifetimes of the $2^{+}_{1}$ and the $4^{+}_{1}$ excited states of 50 Cr have been measured, using the Differential Decay Curve method (DDCM). A derivation is given on how this method can be applied to a differential plunger measurement, in order to measure distances for lifetimes from two different regions of sensitivity at the same time. The commissioning experiment took place at the Cologne FN tandem accelerator, using the reaction 24 Mg( 32 S,4p2n) 50 Cr. Lifetimes, deduced from this measurement, agree well with literature values from earlier measurements.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Reprint of "Selective conversion of CO into ethanol on Cu(511) surface reconstructed from Cu(pc): Operando studies by electrochemical scanning tunneling microscopy, mass spectrometry, quartz crystal nanobalance, and infrared spectroscopy"

A polycrystalline copper, surface-terminated by a well-defined (511)-oriented facet, was electrochemically generated by a series of step-wise surface reconstruction and iterations of mild oxidative-reductive processes in 0.1 M KOH. The electrochemical reduction of CO on the resultant stepped surface was investigated by four surface-sensitive operando methodologies: electrochemical scanning tunneling microscopy (STM), electrochemical quartz crystal nanobalance (EQCN), differential electrochemical mass spectrometry (DEMS), and polarization-modulation infrared spectroscopy (PMIRS). The stepped surface catalyzed the facile conversion of CO into ethanol, the exclusive alcohol product at a low overpotential of -1.06 V (SHE) or - 0.3 V (RHE). Additionally, the chemisorption of CO was found to be a necessary prelude to ethanol production; i.e. the surface coverages, rather than solution concentrations, of CO and its surface-bound intermediates primarily dictate the reaction rates (current densities). Contrary to the expected predominance of undercoordinated step-site reactivity over the coordination chemistry of vicinal surfaces, vibrational spectroscopic evidence reveals the involvement of terrace-bound CO adsorbates during the multi-atomic transformations associated with the production of ethanol.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Resolved Resonance Region Analysis of 206 Pb, 207 Pb, and 208 Pb for Next Generation Lead-Cooled Fast Systems

Recently, great interest has been generated in using lead as a coolant for fast neutron systems and as a result it is important to investigate the ENDF/B-VIII.0 isotopic evaluations that comprise stable le ad. To this end, resonance parameters for 206 Pb, 207 Pb, and 208 Pb were re-evaluated because their resolved reso­nance regions extend beyond 0.5 MeV meaning resonance parameters used in reconstructing cross sections and elastic scattering angular distributions impact fast systems. The impact of resonance parameters is demon­strated by the differences between the evaluations in predicting experimental results from the fully modeled RPI Quasi-Differential Scattering Experiment via MCNPv6.2. In addition, MCNP KCODE calculations of lead-sensitive fast spectra critical benchmarks showed variations of keff on average of 400 pcm, caused solely from differences in elastic scattering angular distributions in 208 Pb. Re-evaluation entailed fitting data with the program SAMMY.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Quantum nondemolition photon counting with a hybrid electromechanical probe

Quantum nondemolition (QND) measurements of photons is a much pursued endeavor in the field of quantum optics and quantum information processing. Here, we propose a hybrid optoelectromechanical platform that integrates a cavity system with a hybrid electromechanical probe for QND photon counting. Building upon a mechanical-mode-mediated nonperturbative electro-optical dispersive coupling, our protocol performs the QND photon counting measurement by means of the current-voltage characteristics of the probe. In particular, we show that the peak voltage shift of the differential conductance is linearly dependent on the photon occupation number, thus providing a sensitive measure of the photon number, especially in the strong optomechanical coupling regime. Here, given that our proposed hybrid system is compatible with state-of-the-art experimental techniques, we discuss its implementations and anticipate applications in quantum optics and polariton physics.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Adaptive Client Selection in Federated Learning: A Network Anomaly Detection Use Case

Federated Learning (FL) has become a ubiquitous approach for training machine learning models on decentralized data, addressing the myriad privacy concerns inherent in traditional centralized methods. However, the efficiency of FL depends on effective client selection and robust privacy preservation mechanisms. Inadequate client selection may lead to suboptimal model performance, while insufficient privacy measures risk exposing sensitive data. This paper proposes a client selection framework for FL that integrates differential privacy and fault tolerance. Our adaptive approach dynamically adjusts the number of selected clients based on model performance and system constraints, ensuring privacy through calibrated noise addition. We evaluate our method on a network anomaly detection use case using the UNSW-NB15 and ROAD datasets. Results show up to a 7% increase in accuracy and a 25% reduction in training time compared to FedL2P. Moreover, we highlight the trade-offs between privacy budgets and model performance, with higher privacy budgets reducing noise and improving accuracy. Our fault tolerance mechanism, while causing a slight performance drop, enhances robustness to client failures. Statistical validation using Mann-Whitney U tests confirms the significance of these improvements (p < 0.05).

Marfo, William [University of Texas at El Paso,Dep↗

Measurements of the Higgs boson inclusive and differential fiducial cross sections in the 4$\ell$ decay channel at $\sqrt{s}$ = 13 TeV

Inclusive and differential fiducial cross sections of the Higgs boson are measured in the H → Z Z * → 4 ℓ ( ℓ = e , μ ) decay channel. The results are based on proton-proton collision data produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector from 2015 to 2018, equivalent to an integrated luminosity of 139 $\hbox {fb}^{-1}$ fb - 1 . The inclusive fiducial cross section for the H → Z Z * → 4 ℓ process is measured to be σ fid = 3.28 ± 0.32 fb, in agreement with the Standard Model prediction of σ fid , SM = 3.41 ± 0.18 fb. Differential fiducial cross sections are measured for a variety of observables which are sensitive to the production and decay of the Higgs boson. All measurements are in agreement with the Standard Model predictions. The results are used to constrain anomalous Higgs boson interactions with Standard Model particles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Longitudinal analysis of host protein serum signatures of treatment and recovery in pulmonary tuberculosis

A better understanding of treatment progression and recovery in pulmonary tuberculosis (TB) infectious disease is crucial. This study analyzed longitudinal serum samples from pulmonary TB patients undergoing interventional treatment to identify surrogate markers for TB-related outcomes. Serum that was collected at baseline and 8, 17, 26, and 52 weeks from 30 TB patients experiencing durable cure were evaluated and compared using a sensitive LC-MS/MS proteomic platform for the detection and quantification of differential host protein signatures relative to timepoint. The global proteome signature was analyzed for statistical differences across the time course and between disease severity and treatment groups. A total of 676 proteins showed differential expression in the serum over these timepoints relative to baseline. Comparisons to understand serum protein dynamics at 8 weeks, treatment endpoints at 17 and 26 weeks, and post-treatment at 52 weeks were performed. The largest protein abundance changes were observed at 8 weeks as the initial effects of antibiotic treatment strongly impacted inflammatory and immune modulated responses. However, the largest number of proteome changes was observed at the end of treatment time points 17 and 26 weeks respectively. Post-treatment 52-week results showed an abatement of differential proteome signatures from end of treatment, though interestingly those proteins uniquely significant at post-treatment were almost exclusively downregulated. Patients were additionally stratified based upon disease severity and compared across all timepoints, identifying 461 discriminating proteome signatures. These proteome signatures collapsed into discrete expression profiles with distinct pathways across immune activation and signaling, hemostasis, and metabolism annotations. Insulin-like growth factor (IGF) and Integrin signaling maintained a severity signature through 52 weeks, implying an intrinsic disease severity signature well into the post-treatment timeframe. Previous proteome studies have primarily focused on the 8-week timepoint in relation to culture conversion status. While this study confirms previous observations, it also highlights some differences. The inclusion of additional end of treatment and post-treatment time points offers a more comprehensive assessment of treatment progression within the serum proteome. Examining the expression dynamics at these later time periods will help in the investigation of relapse patients and has provided indicative markers of response and recovery.

59 BASIC BIOLOGICAL SCIENCES↗

Photolysis of spacecraft contaminants

A molecular beam facility, which was designed to measure photochemical cross-sections, has been constructed at the Athens College science facility. The integration of this vacuum system into an operational photochemical instrument was performed with signal processing consisting of both dc and ac techniques. Of the experiments performed to date on the vacuum ultraviolet photolysis of water vapor, it is apparent that a larger pumping capacity (preferably with differential pumping) is required to improve upon the background signal. Both phase-sensitive detection and ion-counting techniques are recommended for future studies.

Workman, G. L.↗

High-sensitivity circular polarimetry of the Sun, 0.5 - 1.7 microns

Using an isometric (symmetrical) photoelastic-modulator polarimeter and a Cassegrain telescope, broadband polarization measures of the Sun were obtained with unprecedented sensitivity. With an instrumental background of x 10 to the minus 6th power differential effects delta q = V/I of 1 x 10 to the minus 7th power were detectable. Some results: (1) the lambda dependence of broadband circular polarization in spots was observed out to 1.7 mu, extending the visible-light measurements of Illing, Landman, and Mickey. The q drops to of the order of 1 x 10 to the minus 5 power at 1.2 mu (in a strong spot), then rises at 1.6 mu. While molecules or other special mechanisms must play a role in the visible-light polarization, at lambda 1.5 mu the q values seem consistent with gray magneto-opacity. (2) By surveying inactive regions upper limits are set to broadband polarization due to global or deep-seated magnetic fields. For a double-toroidal pattern a differential measure is found, q sub b = (q sub ne + q sub sw - q sub nw - q sub - se) 14, at 1.7 mu, of (+1.2 + or = 0.7) x 10 to the minus 7th power a mean from three series in 1981. Based on a simple estimate by L. Biermann this would correspond to deep-down toroidal fields of or approx 2000 gauss. Extension of this work are discussed.

Kemp, J. C.↗

Osteoblast histogenesis in periodontal ligament and tibial metaphysis during simulated weightlessness

Utilizing the nuclear morphometric assay for osteoblast histogenesis, the effect of simulated weightlessness (SW) on the relative numbers of the periodontal ligament (PDL) osteoblast progenitors and on the total number of osteogenic cells was determined in rats. Weightlessness was simulated by subjecting rats to continuous 30-deg head-down posture using a modified back-harness device of Morey (1979). The response of a partially unloaded, weight-bearing bone, tibial primary spongiosa (PS), was compared to a normally loaded, nonweight-bearing PDL bone. Data indicated a similar differentiation sequence in PS and PDL, which suggests that these bones might be sensitive to the same systemic factors. Preosteoblast numbers were seen to decrease in both nonweight-bearing and weight-bearing bones during SW (compared with rats not exposed to SW), indicating the importance of systemic mediators, such as cephalad fluid shift, physiological stress, and/or growth retardation.

Fielder, Paul J.↗

Precise Measurement of Carbon Dioxide Column by Passive Ground Based Sensor

Over the past four years we have developed a family of differential radiometers based upon the Fabry-Perot interferometers that exhibit very great sensitivity to changes in the atmospheric column of carbon dioxide, oxygen, and water vapor. Our instruments employ a solid Fabry-Perot etalon that is tuned to the proper wavelength by changing its temperature. The thickness of the etalon has been selected so that its multiple pass bands align with regularly space absorption features of the molecule under investigation. Using multiple absorption features improves the optical throughput of the instrument and improves the stability of the instrument response with respect to environmental changes. We are presently working to extend this technique to the carbon 13 isotope of carbon dioxide and to methane. Our instruments are intrinsically rugged and can be fabricated in a small package at relatively low cost.. As such they hold promise for widespread use in ground based networks for calibration and validation of satellite instruments such as OCO and GOSAT. Results will be presented for long term ground based operations of these systems. The effects of atmospheric scattering, pointing errors, pressure broadening and temperature effects will be discussed with regard to achieving precision better than .5% required for validation of carbon dioxide column measured from space. Finally we will outline the approach for extension of this methodology to additional molecular species of interest.

Heaps, William S.↗

Diode injection - seeded, 940 nanometer (nm), titanium - sapphire laser for H2O DIAL (differential absorption lidar), measurements

Differential absorption of laser radiation by various molecular species represents both a selective and a sensitive method of measuring specific atmospheric constituents. DIAL measurements can be carried out via two different means. Both involve using two laser pulses with slightly different wavelengths (lambda), (one lambda at a strong absorption line of the molecule of interest, the other detuned into the wing of the line), and comparing the attenuation of the pulses. One approach relies on scattering of the radiation from some conveniently located topographical target. In the other technique elastic scattering from atmospheric aerosols and particulates is used to return the radiation to the lidar receiver system. This case is referred to as the differential absorption and scattering technique, and is the technique we are interested in to measure water vapor at 940 nm. The 940 nm wavelength is extremely desirable to atmospheric scientist interested in accurate DIAL measurements of H2O in the upper and lower troposphere. Simulated measurements using approximately 940 nm and 815 nm lasers at a range of altitudes and experimental conditions are shown. By offering access to larger absorption cross-sections, injected seeded, 940 nm DIAL laser transmitters would allow for more accurate water profile measurements at altitudes from 6 to 16 km than is currently possible with 730 nm and 815 nm DIAL laser transmitters. We have demonstrated the operation of an injected seeded titanium-sapphire (TS) laser operating at approximately 940 nm with an energy of more than 90 mJ per pulse. The TS laser is pumped by a commercial, 600 mJ, 532 nm, 10 Hz Nd:YAG laser. The slope efficiency of the laser using a flat 50 percent R output coupler and a 10 m end-mirror is shown. The laser was injected seeded with a CW, AlGaAs, semiconductor diode laser which had an output of 83 mW. The CW diode seed beam was introduced into the TS laser cavity through a HR end-mirror. When the diode beam is aligned to the TS resonator, it controls the TS laser output wavelength and its spectral line width with the required resolution for DIAL applications. This work supports the need for the development of 940 nm, titanium-sapphire DIAL transmitters.

Miller, George E.↗