Hasil untuk "physics.ed-ph"

Y. Surendranath, M. Kanan, D. Nocera

S. Bian, Imali A. Mudunkotuwa, T. Rupasinghe et al.

A. Pezzulo, X. Tang, M. J. Hoegger et al.

Cystic fibrosis (CF) is a life-shortening disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Although bacterial lung infection and the resulting inflammation cause most of the morbidity and mortality, how the loss of CFTR function first disrupts airway host defence has remained uncertain. To investigate the abnormalities that impair elimination when a bacterium lands on the pristine surface of a newborn CF airway, we interrogated the viability of individual bacteria immobilized on solid grids and placed onto the airway surface. As a model, we studied CF pigs, which spontaneously develop hallmark features of CF lung disease. At birth, their lungs lack infection and inflammation, but have a reduced ability to eradicate bacteria. Here we show that in newborn wild-type pigs, the thin layer of airway surface liquid (ASL) rapidly kills bacteria in vivo, when removed from the lung and in primary epithelial cultures. Lack of CFTR reduces bacterial killing. We found that the ASL pH was more acidic in CF pigs, and reducing pH inhibited the antimicrobial activity of ASL. Reducing ASL pH diminished bacterial killing in wild-type pigs, and, conversely, increasing ASL pH rescued killing in CF pigs. These results directly link the initial host defence defect to the loss of CFTR, an anion channel that facilitates HCO3− transport. Without CFTR, airway epithelial HCO3− secretion is defective, the ASL pH falls and inhibits antimicrobial function, and thereby impairs the killing of bacteria that enter the newborn lung. These findings suggest that increasing ASL pH might prevent the initial infection in patients with CF, and that assaying bacterial killing could report on the benefit of therapeutic interventions.

J. Koufman

I. Tannock, D. Rotin

D. Houben, Laurent Evrard, P. Sonnet

Saba M. Ali, G. Yosipovitch

The "acid mantle" is a topic not only of historical interest, but also of clinical significance and has recently been linked to vital stratum corneum function. Despite compelling basic science evidence placing skin pH as a key factor in barrier homeostasis, stratum corneum integrity, and antimicrobial defense, application of the acid mantle concept in clinical care is lacking. We review recent basic science investigations into skin pH, discuss skin disorders characterized by aberrant pH, and finally discuss practical application for preservation of the acid mantle. Recognizing factors that alter skin pH and selecting products that preserve the acid mantle is of prime importance in treating dermatologic patients.

Kun Wang, Jun Yin, D. Shen et al.

Hongyu Guo, Lu Xu, A. Bougiatioti et al.

Abstract. Particle water and pH are predicted using meteorological observations (relative humidity (RH), temperature (T)), gas/particle composition, and thermodynamic modeling (ISORROPIA-II). A comprehensive uncertainty analysis is included, and the model is validated. We investigate mass concentrations of particle water and related particle pH for ambient fine-mode aerosols sampled in a relatively remote Alabama forest during the Southern Oxidant and Aerosol Study (SOAS) in summer and at various sites in the southeastern US during different seasons, as part of the Southeastern Center for Air Pollution and Epidemiology (SCAPE) study. Particle water and pH are closely linked; pH is a measure of the particle H+ aqueous concentration and depends on both the presence of ions and amount of particle liquid water. Levels of particle water, in turn, are determined through water uptake by both the ionic species and organic compounds. Thermodynamic calculations based on measured ion concentrations can predict both pH and liquid water but may be biased since contributions of organic species to liquid water are not considered. In this study, contributions of both the inorganic and organic fractions to aerosol liquid water were considered, and predictions were in good agreement with measured liquid water based on differences in ambient and dry light scattering coefficients (prediction vs. measurement: slope = 0.91, intercept = 0.5 μg m−3, R2 = 0.75). ISORROPIA-II predictions were confirmed by good agreement between predicted and measured ammonia concentrations (slope = 1.07, intercept = −0.12 μg m−3, R2 = 0.76). Based on this study, organic species on average contributed 35% to the total water, with a substantially higher contribution (50%) at night. However, not including contributions of organic water had a minor effect on pH (changes pH by 0.15 to 0.23 units), suggesting that predicted pH without consideration of organic water could be sufficient for the purposes of aqueous secondary organic aerosol (SOA) chemistry. The mean pH predicted in the Alabama forest (SOAS) was 0.94 ± 0.59 (median 0.93). pH diurnal trends followed liquid water and were driven mainly by variability in RH; during SOAS nighttime pH was near 1.5, while daytime pH was near 0.5. pH ranged from 0.5 to 2 in summer and 1 to 3 in the winter at other sites. The systematically low pH levels in the southeast may have important ramifications, such as significantly influencing acid-catalyzed reactions, gas–aerosol partitioning, and mobilization of redox metals and minerals. Particle ion balances or molar ratios, often used to infer pH, do not consider the dissociation state of individual ions or particle liquid water levels and do not correlate with particle pH.

P. Swietach, R. Vaughan-Jones, A. Harris et al.

Katherine M. Strickler, A. Fremier, C. Goldberg

P. Lund, A. Tramonti, D. De Biase

S. Percival, Sara M. McCarty, J. Hunt et al.

W. Moolenaar, R. Tsien, P. Saag et al.

Nishil Savla

Neutrino oscillations arise from quantum interference between neutrino mass eigenstates and are governed by the PMNS matrix. Although this is an intrinsically quantum phenomenon, its mathematical structure is analogous to systems of coupled classical oscillators. In this work, a three--pendulum system connected by springs is constructed as a classical analog of three--flavor neutrino oscillations. Measurements of amplitude transfer, normal--mode structure, and beat frequencies are used to extract a mechanical mixing matrix, which is compared with the structure of the PMNS matrix under the assumption of zero CP violation. A scaling relation linking mechanical time evolution to the neutrino \(L/E\) behavior is derived, clarifying the scope and limitations of the analogy. The experiment demonstrates how abstract concepts of neutrino mixing can be visualized using simple and accessible classical systems, offering both pedagogical value and a qualitative understanding of flavor oscillation dynamics.

Taha Anwar

The Standard Model of particle physics is built on the principle of local gauge symmetry. This work provides a pedagogical introduction for advanced undergraduates by using quantum electrodynamics (QED) as the simplest example of a gauge theory. Beginning with the Lagrangian formulation of classical mechanics, special relativity, and basic quantum mechanics, we develop classical field theory, reformulate electromagnetism in covariant form, introduce the Dirac equation for spin 1/2 particles, and finally arrive at the gauge principle. By showing how the requirement of local U(1) invariance leads naturally to the electromagnetic interaction, we illustrate the essential logic behind gauge theories and highlight the conceptual structure that underlies the Standard Model Lagrangian.

Binbin Liu, P. Mørkved, Å. Frostegård et al.

The N(2)O : N(2) product ratio of denitrification is negatively correlated with soil pH, but the mechanisms involved are not clear. We compared soils from field experiments where the pH had been maintained at different levels (pH 4.0-8.0) by liming (> or = 20 years), and quantified functional gene pools (nirS, nirK and nosZ), their transcription and gas kinetics (NO, N(2)O and N(2)) of denitrification as induced by anoxic incubation with and without a carbon substrate (glutamate). Denitrification in unamended soil appeared to be based largely on the activation of a pre-existing denitrification proteome, because constant rates of N(2) and N(2)O production were observed, and the transcription of functional genes was below the detection level. In contrast, glutamate-amended soils showed sharp peaks in the transcripts of nirS and nosZ, increasing the rates of denitrification and pH-dependent transient accumulation of N(2)O. The results indicate that the high N(2)O : N(2) product ratio at low pH is a post-transcriptional phenomenon, because the transcription rate of nosZ relative to that of nirS was higher at pH 6.1 than at pH 8.0. The most plausible explanation is that the translation/assembly of N(2)O reductase is more sensitive to low pH than that of the other reductases involved in denitrification.

J. K. Freericks

The von Neumann theory of measurement, based on an entanglement of the quantum observable with a classical machine followed by decoherence or collapse, does not readily apply to most measurements of momentum. Indeed, how we measure the momentum of a quantum particle is not even discussed in most quantum mechanics textbooks. Instead, we often teach the lore that position and momentum cannot be measured at the same time. Yet, most ways to measure momentum actually involve measuring position to infer momentum. In this tutorial review, I examine real experiments that measure momentum and describe how one can improve our teaching of the theory of measurement when we focus on real experiments, rather than abstract mathematical models of measurement.

D. Johnson, T. Kanao, S. Hedrich et al.

Many different species of acidophilic prokaryotes, widely distributed within the domains Bacteria and Archaea, can catalyze the dissimilatory oxidation of ferrous iron or reduction of ferric iron, or can do both. Microbially mediated cycling of iron in extremely acidic environments (pH < 3) is strongly influenced by the enhanced chemical stability of ferrous iron and far greater solubility of ferric iron under such conditions. Cycling of iron has been demonstrated in vitro using both pure and mixed cultures of acidophiles, and there is considerable evidence that active cycling of iron occurs in acid mine drainage streams, pit lakes, and iron-rich acidic rivers, such as the Rio Tinto. Measurements of specific rates of iron oxidation and reduction by acidophilic microorganisms show that different species vary in their capacities for iron oxido-reduction, and that this is influenced by the electron donor provided and growth conditions used. These measurements, and comparison with corresponding data for oxidation of reduced sulfur compounds, also help explain why ferrous iron is usually used preferentially as an electron donor by acidophiles that can oxidize both iron and sulfur, even though the energy yield from oxidizing iron is much smaller than that available from sulfur oxidation. Iron-oxidizing acidophiles have been used in biomining (a technology that harness their abilities to accelerate the oxidative dissolution of sulfidic minerals and thereby facilitate the extraction of precious and base metals) for several decades. More recently they have also been used to simultaneously remediate iron-contaminated surface and ground waters and produce a useful mineral by-product (schwertmannite). Bioprocessing of oxidized mineral ores using acidophiles that catalyze the reductive dissolution of ferric iron minerals such as goethite has also recently been demonstrated, and new biomining technologies based on this approach are being developed.

J. Ban, Mijung Lee, W. Im et al.