Net Proton Research Articles

Cumulants of multiple conserved charges and global conservation laws

We analyze the behavior of cumulants of conserved charges in a subvolume of a thermal system with exact global conservation laws by extending a recently developed subensemble acceptance method (SAM) [1] to multiple conserved charges. Explicit expressions for all diagonal and off-diagonal cumulants up to sixth order that relate them to the grand canonical susceptibilities are obtained. The derivation is presented for an arbitrary equation of state with an arbitrary number of different conserved charges. The global conservation effects cancel out in any ratio of two second order cumulants, in any ratio of two third order cumulants, as well as in a ratio of strongly intensive measures Σ and ∆ involving any two conserved charges, making all these quantities particularly suitable for theory-to-experiment comparisons in heavy-ion collisions. We also show that the same cancellation occurs in correlators of a conserved charge, like the electric charge, with any non-conserved quantity such as net proton or net kaon number. The main results of the SAM are illustrated in the framework of the hadron resonance gas model. We also elucidate how net-proton and net-Λ fluctuations are affected by conservation of electric charge and strangeness in addition to baryon number.

The STAR Detector Upgrades for the BES-II and at Forward Rapidity

The Beam Energy Scan Phase II program (BES-II) at the Relativistic Heavy Ion Collider (RHIC) is examining the center-of-mass collision energy region from 7.7 GeV to 19.6 GeV which was determined from the results of BES-I. Key measurements such as the net proton kurtosis, the directed flow and the dilepton production are possible during BES-II with an order of magnitude better statistics due to the Low Energy RHIC electron Cooling (LEReC) upgrade and several STAR detector upgrades. Beyond BES-II, the STAR Collaboration is currently designing, constructing, and installing a suite of new detectors in the forward rapidity region (2.5 < η < 4), enabling a program of novel measurements in pp, pA and AA collisions. To fully explore this physics, the forward rapidity region needs superior detection capability for neutral pions, photons, electrons, jets and leading hadrons by adding charged particle tracking and electromagnetic and hadronic calorimetry to STAR's capabilities at forward rapidity. In this proceedings, we will present the details on the STAR detector upgrades for the BES-II and at forward rapidity. The Cold QCD physics opportunities will also be discussed.

Stability Analysis of GMZ Bentonite Colloids: Aggregation Mechanism Transition and the Edge Effect in Strongly Alkaline Conditions

In this study, the basic physicochemical properties (composition, morphology and surface charge) of the colloids obtained from Gaomiaozi (GMZ) bentonite were analyzed and photon correlation spectroscopy (PCS) tests were conducted for looking into the effects of ionic strength and pH on the stability. The results showed that the bentonite colloids were composed primarily of montmorillonite and cristobalite, and remained stable up to at least 8 months in pure water system, and its self-coagulation was negligible. The titration curves of the bentonite colloids showed a typical titration shape of montmorillonite clay, while a common intersection at the point of zero charge (PZC) around 9.5 and a slightly higher net proton sorption capacity compared with bulk form of GMZ bentonite reported in the literature were observed. The stability was strongly PZC dependent, around which the critical coagulation concentration (CCC) value rose rapidly with increasing pH stemming from the transition of different aggregation mechanisms. Further, a more important effect of the edge charge in strongly alkaline conditions was found to exist. This work can be helpful for better understanding the stability characterization of layered clay colloids and provides a valuable reference for safety assessments of the deep geological disposal repository for high-level radioactive wastes.

Binomial acceptance corrections for particle number distributions in high-energy reactions

The binomial acceptance correction procedure is studied for particle number distributions detected in high energy reactions in finite regions of the momentum space. We present acceptance correction formulas for scaled variance, skewness, and kurtosis. Our considerations include various specific types of particles - positively or negatively charged, baryons and antibaryons - as well as conserved charges, namely, the net baryon number and electric charge. A simple model with effects of exact charge conservation, namely the Bessel distribution, is studied in some detail where effects of multi-particle correlations are present. The accuracy of the binomial filter is studied with UrQMD model simulations of inelastic proton-proton reactions. Binomial acceptance correction procedure works well when used inside a small region of phase space as well as for certain efficiency corrections, in particular for constructing net proton fluctuation from net baryon ones. Its performance is less accurate when applied to obtain UrQMD fluctuations in a finite rapidity window from fluctuations in the full $4\pi$ space.

The ebb and flow of protons: A novel approach for the assessment of estuarine and coastal acidification

The acidification of estuarine and coastal waters is a consequence of both natural (e.g., aerobic respiration) and anthropogenic (e.g., combustion of fossil fuels, eutrophication) processes and can negatively impact the surrounding ecosystems. Until recently it was difficult to accurately measure pH, and thus total proton concentrations ([HT+]), when salinities vary significantly and rapidly as a consequence of tidal mixing. Proton production and transport are ultimately responsible for acidification in nearshore environments, and the uncertainty surrounding proton concentrations measured at high frequency has hindered our understanding of the net impact of global and local processes on estuarine and coastal acidification. Here, we quantify the rate of proton exchange between an estuary and bay to assess the extent of acidification by using the novel combination of high frequency pHT (total hydrogen ion concentration scale) data from an autonomous SeapHOx™ sensor and continuous tidal discharge measurements made between the eutrophic Murderkill Estuary and Delaware Bay. Proton fluxes reverse with each tide. However, the net non-tidal proton fluxes are directed upstream and display seasonal changes in magnitude. Our results indicate that Delaware Bay contributes to the acidification of the Murderkill Estuary, yet the degree of acidification is reduced in the summer. Using proton concentrations measured at high temporal resolution to calculate proton fluxes provides a new and relatively simple approach for quantifying the acidification of dynamic nearshore environments.

Role of baryon number conservation in measurements of fluctuations

I discuss the role and impact of net-baryon number conservation in measurements of net proton fluctuations in heavy-ion collisions. I show that the magnitude of the fluctuations is entirely determined by the strength of two particle correlations. At LHC and top RHIC energy, this implies the fluctuations are proportional to the integral of the balance function (BF), $B^{p\bar p}$ of protons and anti-protons, while in the context of the RHIC beam energy scan (BES), one must also account for correlations of "stopped" protons. The integral of $B^{p\bar p}$ measured in a $4\pi$ detector depends on the relative cross-sections of processes yielding $p\bar p$ and those balancing the proton baryon number via the production of other anti-baryons. The accepted integral of $B^{p\bar p}$ further depends on the shape and width of the BF relative to the width of the acceptance. The magnitude of the measured second order cumulant of net proton fluctuations thus has much less to do with QCD susceptibilities than with the creation/transport of baryons and anti-baryons in heavy-ion collisions, and most particularly the impact of radial flow on the width of the BF. I thus advocate that net-proton fluctuations should be studied by means of differential BF measurements rather integral correlators.

Understanding the effect of carbon surface chemistry on adsorption of perfluorinated alkyl substances

The adsorption of perfluorooctanoic acid (PFOA) and perfluorooctylsulfonic acid (PFOS) on various activated carbon felts (ACFs) was studied and related to their surface characteristics. The adsorption isotherms of the ACFs studied differ widely in terms of adsorption affinities as well as maximum loadings. Cation and anion exchange capacities (CEC and AEC) at pH 7, as well as point of zero net proton charge (PZC), were identified as good indicators for understanding of each adsorbent’s behavior towards the perfluorinated alkyl substances (PFAS) in their anionic state. Maximum loadings of the two PFAS are in all cases equal to or lower than the AEC of the ACFs. The superposition of hydrophobic interactions and electrostatic attraction between PFAS anions and positively charged sites of ACF leads to exceptionally high adsorption affinity (Kd up to 108 L/kg). In this respect, positive charges created by proton adsorption to π-electron-rich regions on the basal plane of carbon are more important than basic oxygen-containing groups. The effect of inorganic ions on adsorption of PFAS is variable and is also influenced by the surface chemistry of the ACFs. Dissolved natural organic matter did not significantly affect PFAS adsorption most likely due to size exclusion exerted by the micropores of the ACFs.

Radiative Parton Energy Loss and Baryon Stopping in AA Collisions

We study the radiative energy loss contribution to proton stopping in $AA$ collisions. The analyses is performed within the light-cone path integral approach to induced gluon emission. We have found that the radiative correction can fill in partly the midrapidity dip in the net proton rapidity distribution in $AA$ collisions at $\sqrt{s}\sim 10$ GeV. We argue that at $\sqrt{s}\sim 10$ GeV the net proton fluctuations at midrapidity may be dominated by the initial fluctuations of the proton flow, which, to a good accuracy, should be binomial.

Altering mitochondrial bioenergetic efficiency

Mitochondrial oxidative phosphorylation (OXPHOS) accounts for the vast majority of daily energy expenditure, making the efficiency at which this process occurs a potential attractive target for treating diseases associated with positive energy balance. Organic cations are a class of small carbon molecules that carry a formal charge on a nitrogen or phosphorus atom and/or contain an aliphatic amine group which protonates at physiological pH. Well studied examples from each class include the anti‐diabetic compounds berberine (+1 charge) and metformin (+2 charge at pH of 7). These compounds, like all cations, are naturally drawn to the mitochondrial matrix by the negative potential across the inner membrane. According to Nernst equilibria, the accumulation of a positively charged compound into the mitochondrial matrix is predicted to reduce the net proton motive force (Δp) available to drive ATP synthesis. In an in vitro assay of respiratory capacity, the reduced Δp will manifest as a decrease in the maximal rate at which ATP can be synthesized and therefore the maximal rate at which O2 is consumed. However, in vivo where the interplay between energetic driving forces and flux continuously adjusts to demand (e.g., ATP turnover rate), a decrease in Δp is predicted to decrease the efficiency at which those demands can be met, requiring a greater flux rate through OXPHOS and therefore energy expenditure per unit of time. Testing of &gt;15 different organic cations in isolated mitochondria thus far has revealed remarkably similar, dose‐dependent decreases in NAD‐linked ADP‐stimulated respiration, H2O2 emission, and the Δp under different rates of clamped respiration. Additional data will be presented on the dose‐dependent impact of acute and chronic administration of organic cations in vivo in both mice and rats. Together, the data highlight a novel therapeutic model by which organic cations mitigate obesogenic conditions by altering the interplay among energetic driving forces to decrease OXPHOS efficiency. Organic cations may serve as a potential novel class of drugs for the prevention and/or treatment of diseases stemming from chronic metabolic imbalance.Support or Funding InformationNational Institutes of Health Grants R01 DK096907This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Critical point of nuclear matter and beam-energy dependence of net-proton number fluctuations

The beam energy dependence of net baryon number susceptibilities is studied in the framework of the hadron resonance gas model with the attractive and repulsive van der Waals interactions between baryons. The collision energy dependences for the skewness $S\sigma$ and kurtosis $\kappa\sigma^2$ deviate significantly from the Poisson baseline and demonstrate the existence of rich structures at moderate collision energies. This behavior may result from the critical end point of the nuclear liquid-gas first order phase transition. In particular, $\kappa\sigma^2$ shows a non-monotonic energy dependence, and, in contrast to the standard scenario for the QCD critical point, it does not decrease at low collision energies. It is also found that the measurable net proton fluctuations differ significantly from the net baryon fluctuations when interactions between baryons cannot be neglected. The results are compared with the experimental net proton number fluctuations measured by the STAR collaboration.

Change of the point of zero net proton charge (pHPZNPC) of clay minerals with ionic strength

In a system where protons and hydroxide ions are the only aqueous species, the point of zero net proton charge (pHPZNPC) of a mineral defines the pH at which the positively and negatively charged functional groups on its surface are equal (Drever, 1997). Ascertaining the pHPZNPC of clay minerals, a ubiquitous component in soils, sediment and rivers, is useful in predicting its electrostatic interactions with charged aqueous species, colloids, and bacteria. While the pHPZNPC values of most clays have been reported, the variation of pHPZNPC with changing solution ionic strength (IS) and the mathematic relationship between them are not well-understood but critical in assessing the surface reactivity of clays in aqueous solutions ranging from freshwater to brines. To address this gap, we studied the relationship of the pHPZNPC of three clay minerals (kaolinite, illite, and montmorillonite) at seven ionic strengths (from 0.001 to 0.1 M). Titration data for each clay were used to calculate the pHPZNPC by two methods previously documented in literature: (1) using the difference between the blank titration and clay titrations, and (2) by the difference between the number of protons added during titration and the number of protons remaining in solution. The results show that: (1) unlike simple metal oxides (e.g., hematite, gibbsite, quartz), titration curves of clay minerals at different IS do not intersect at a common pHPZNPC value; (2) the pHPZNPC for kaolinite is around 5.6 to 6.6 while the pHPZNPC for illite and montmorillonite is in the range of 9 to10; (3) the pHPZNPC value decreases systematically with increasing IS for all three clay minerals studied; and (4) the change of pHPZNPC is linear with log(IS). A third method using surface complexation modeling (SCM) approach was applied to calculate the pHPZNPC of the clay minerals, and the results match well with Method 2. Our results allow for a more accurate estimation of clay surface charge property in aqueous environment, which, in turn, will improve model predictions of the adsorption of charged species in systems in which ionic strength changes.

Regulation of clay particles charge for design of protective electrokinetic barriers

Coupled electrokinetic protective reactive barriers (PRB) are considered as a perspective technology for the treatment of contaminated groundwater. Design of PRB is directly connected with a problem of barrier material choice. Clays can be considered as an appropriate material due to high adsorptive properties and relative cheapness. The barrier internals are formed by clay surface charge properties. We revealed that acidic and alkaline treatment of clay is an effective way to affect its protective properties so that clay can be used to treat various pollutants. Surface charge and electrokinetic properties of clays were characterized by point of zero charge (p.z.c.), point of zero net proton charge (p.z.n.p.c.) and ζ-potential at different pH. Suspensions of 3 main clay types were studied by microelectrophoresis and potentiometric titration methods. At pH > p.z.n.p.c. clayey barrier adsorbs predominantly cationic toxicants and at pH < p.z.c. – anionic ones. The barrier is seemed to be the least effective in pH range between p.z.c. and p.z.n.p.c. Given the physicochemical and electrokinetic parameters, the most efficient clays for barrier design are Cambrian illite and all montmorillonite clays.

Clay particle charging in apolar media

Abstract Advancements in electrophoretic displays (e.g., the Amazon Kindle®) and new high-quality printing technologies (e.g., HP Indigo®) have been made possible by the ability to control and understand particle charging in apolar media. While previous work has investigated the acid-base charging mechanisms of oxides and similar particles which have only one charging mechanism in water, the purpose of this study was to determine if and how clay particles, which have two known aqueous charging mechanisms, charge in apolar media. Characterization of kaolinite and montmorillonite surface charging properties and mechanisms were conducted in apolar media utilizing different surfactants. It was found that clay particle charging behavior as a function of surfactant concentration mimicked the expected trend of previously studied oxides, which can charge only via an acid-base mechanism. Furthermore, by comparing the point of zero charge of the edge groups (edge PZC) or the point of zero net proton charge (PZNPC) of the clay particle to the empirical effective pH (pHEff) of the surfactant, the polarity of the particle charge can be predicted. In addition to particle charging, it was shown that the surfactants also improve the stability against aggregation and settling of the particles.

Numerical investigation of the effect of net charge injection on the electric field deviation in a TE CO2 laser

In this report, the distribution of and deviation in the electric field were investigated in the active medium of a TE CO2 laser. The variation in the electric field is due to injection of net electron and proton charges as a plasma generator. The charged-particles beam density is assumed to be Gaussian. The electric potential and electric field distribution were simulated by solving Poisson’s equation using the SOR numerical method. The minimum deviation of the electric field obtained was about 2.2% and 6% for the electrons and protons beams, respectively, for a charged-particles beam-density of 106 cm-3. This result was obtained for a system geometry ensuring a mean-free-path of the particles beam of 15 mm. It was also found that the field deviation increases for a the mean-free-path smaller than that or larger than 25 mm. Moreover, the electric field deviation decreases when the electrons beam density exceeds 106 cm-3.

Pools and solubility of soil phosphorus as affected by liming in long-term agricultural field experiments

Published laboratory studies suggest minimum solubility of soil phosphorus (P) in the pH range traditionally considered as the target for lime applications on agricultural land. However, the potential significance of these results for the timescale relevant in practical agriculture remains to demonstrate. We revisited four long-term (50–76years) agricultural lime experiments located on Quaternary deposits with topsoil texture ranging from silt loam to silty clay and initial pH between 5.0 and 6.0. Crop uptake data and desorption experiments in the laboratory indicated that liming enhanced the solubility of P added with fertiliser in the decades following the application of lime. An empirical mass-balance model demonstrated that changes in acetate-lactate extractable P (‘P-AL’), previously shown to be related to reactive phosphate adsorbed on soil mineral surfaces, was proportional to field P balances (fertiliser P – harvested P) and inversely proportional to the net proton load to the soil. Extraction data suggest that liming enhanced the incorporation of silica in non-crystalline sesquioxides, which in turn inhibited the conversion of fertiliser P into less extractable forms by migration of P to inside the oxides. Liming induced a lowering of the C/N ratio in one of the experiments, suggesting stimulated decomposition of soil organic matter. However, lime applications did not lead to a decline in the pool of soil organic P, as measured by the combustion method. Mass-balance considerations showed that changes in organic-matter input due to liming were unlikely to result in observable changes in the pool of soil organic P.

Freezeout systematics due to the hadron spectrum

We investigate systematics of the freezeout surface in heavy ion collisions due to the hadron spectrum. The role of suspected resonance states that are yet to be confirmed experimentally in identifying the freezeout surface has been investigated. We have studied two different freezeout schemes - unified freezeout scheme where all hadrons are assumed to freezeout at the same thermal state and a flavor dependent sequential freezeout scheme with different freezeout thermal states for hadrons with or without valence strange quarks. The data of mean hadron yields as well as scaled variance of net proton and net charge distributions have been analysed. We find the freezeout temperature $T$ to drop by $\sim5\%$ while the dimensionless freezeout parameters $\mu_B/T$ and $VT^3$ ($\mu_B$ and $V$ are the baryon chemical potential and the volume at freezeout respectively) are insensitive to the systematics of the input hadron spectrum. The observed hint of flavor hierarchy in $T$ and $VT^3$ with only confirmed resonances survives the systematics of the hadron spectrum. It is more prominent between $\sqrt{s_{NN}}\sim10 - 100$ GeV where the maximum hierarchy in $T\sim10\%$ and $VT^3\sim40\%$. However, the uncertainties in the thermal parameters due to the systematics of the hadron spectrum and their decay properties do not allow us to make a quantitative estimate of the flavor hierarchy yet.

Role of Cation Structures for Energetic Performance of Hypergolic Ionic Liquids

In recent years, novel hypergolic ionic liquids (HILs) have attracted much attention in energy and fuel fields due to their prominent advantages, including low volatility, high thermal stability, excellent energetic performances, and outstanding designability. To investigate the influence of cation structure on the properties and performances of HILs, nine different imidazolium dicyanamide-based ionic liquids were prepared, characterized, and evaluated as potential hypergolic fuels. The heat of formation and the net proton transfer (NPT) energies were calculated by an optimized theoretical model. Ignition delay (ID) time was obtained by a droplet test with a high-speed camera. The results suggest that all ionic liquids possess high density (>1 g/mL) and high thermal stability. 1-Ethyl-3-methyl imidazolium dicyanamide has the lowest viscosity of 15.2 cP, and 1-allyl-3-methyl imidazolium dicyanamide has the shortest ID time of 25 ms. The viscosities, densities, and energy properties depend on the structure ...

Baryon number fluctuations in chiral effective models and their phenomenological implications

We study the critical properties of net-baryon-number fluctuations at the chiral restoration transition in a medium at finite temperature and net baryon density. The chiral dynamics of quantum chromodynamics (QCD) is modeled by the Polykov-loop extended Quark-Meson Lagrangian, that includes the coupling of quarks to vector meson and temporal gauge fields. The Functional Renormalization Group is employed to properly account for the $O(4)$ criticality at the phase boundary. We focus on the properties and systematics of ratios of the net-baryon-number cumulants $\chi_B^n$, for ${1\leq n\leq 6}$, near the phase boundary. The results are presented in the context of the recent experimental data of the STAR Collaboration on fluctuations of the net proton number in heavy ion collisions at RHIC. We show that the model results for the energy dependence of the cumulant ratios are in good overall agreement with the data, with one exception. At center-of-mass energies below ${19.6\;\mathrm{GeV}}$, we find that the measured fourth-order cumulant deviates considerably from the model results, which incorporate the expected $O(4)$ and $Z(2)$ criticality. We assess the influence of model assumptions and in particular of repulsive vector-interactions, which are used to modify the location of the critical endpoint in the model, on the cumulants ratios. Finally, we discuss a possibility to test to what extent the fluctuations are affected by nonequilibrium dynamics by comparing certain ratios of cumulants.

Adsorption of Antimonate by Kaolinite

Core Ideas Sb(V) adsorption by kaolinite is pH and ionic strength dependent, with adsorption decreasing with increasing pH and ionic strength. Sb(V) adsorption is hysteretic in acidic systems, but reversible in alkaline. Adsorbed Sb(V) generates a downward shift in the isoelectric point and an upward shift in the point of zero net proton charge. Phosphate decreases Sb(V) adsorption, but the influence of sulfate is minimal. The macroscopic findings indicate that Sb(V) is retained by innersphere in acidic and outersphere in neutral to alkaline systems. The environmental fate and behavior of antimony (Sb) is controlled by adsorption processes at the solid–solution interface of surface‐reactive solids. One such solid is kaolinite, which bears the aluminol (≡AlOH) surface functional group. The objectives of this study are to characterize antimonate [Sb(V) in the Sb(OH)6– species] adsorption by kaolinite as a function of pH, ionic environment, and competing ligands (PO4 and SO4); to describe the reversibility of the adsorption and the influence of adsorbed Sb(V) on the surficial properties of kaolinite; and to develop predictive surface complexation models. The results of this study show adsorbed Sb(V) is at a maximum in strongly acidic suspensions, and retention decreases with increasing pH and ionic strength. Adsorption is hysteretic in pH &lt; 5 suspensions, becoming reversible with increasing pH. The point of zero net proton charge (PZNPC) increases from 4.5 in KNO3 to 5.6 in KSb(OH)6. Correspondingly, the isoelectric point decreases from 4.5 in KNO3 to &lt;3 in KSb(OH)6. The macroscopic findings indicate that Sb(V) is retained by a combination of inner and outersphere mechanisms, with the former dominating in acidic suspensions. The inclusion of SO4 had little impact on the retention of Sb(V); however, PO4 reduced Sb(V) retention. The inclusion of both inner‐ and outersphere complexes in the triple layer surface complexation model (TLM) provided an adequate description of the Sb(V) adsorption envelopes. Further, the TLM successfully predicted ligand retention in competitive systems without re‐optimization.

Dinuclear Rhenium Complex with a Proton Responsive Ligand as a Redox Catalyst for the Electrochemical CO2 Reduction

Herein, we present the reduction chemistry of a dinuclear α-diimine rhenium complex, 1, [Re2(L)(CO)6Cl2], with a proton responsive ligand and its application as a catalyst in the electrochemical CO2 reduction reaction (L = 4-tert-butyl-2,6-bis(6-(1H-imidazol-2-yl)-pyridin-2-yl)phenol). The complex has a phenol group in close proximity to the active center, which may act as a proton relay during catalysis, and pyridine-NH-imidazole units as α-diimine donors. The complex is an active catalyst for the electrochemical CO2 reduction reaction. CO is the main product after catalysis, and only small amounts of H2 were observed, which can be related to the ligand reactivity. The ic/ip ratio of 20 in dimethylformamide (DMF) + 10% water for 1 points to a higher activity with regard to [Re(bpy)(CO)3Cl] in MeCN/H2O, albeit 1 requires a slightly larger overpotential (bpy = 2,2'-bipyridine). Spectroscopic and theoretical investigations revealed detailed information about the reduction chemistry of 1. The complex exhibits two reduction processes in DMF, and each process was identified as a two-electron reduction in the absence of CO2. The first 2e- reduction is ligand based and leads to homolytic N-H bond cleavage reactions at the imidazole units of 1, which is equal to a net double proton removal from 1 forming [Re2(LH-2)(CO)6Cl2]2-. The second 2e- reduction process has been identified as an O-H bond cleavage reaction at the phenol group, removal of chloride ions from the coordination spheres of the metal ions, and a ligand-centered one-electron reduction of [Re2(LH-3)(CO)6Cl]2-. In the presence of CO2, the second reduction process initiates catalysis. The reduced species is highly nucleophilic and likely favors the reaction with CO2 instead of O-H bond cleavage.