34,909 research outputs found
Physiological adaptation of two unicellular green algae to pH stress.
No full textTwo marine algae, Dunaliella parva and Chlorococcum submarinum were selected to study the effect of pH stress on single celled algae. D. parva has been well characterised physiologically, but not with regards to pH stress. C submarinum has not been so extensively studied, but is known to grow over a wide pH range from pH 4.5 to 10.5. It was of prime importance that the algal cells were grown at the desired extreme values of external pH. Problems were encountered at high levels of pH but were overcome by growing the algae in a fermenter set up as a batch culture. This method of growth was used for both algae at extreme values of external pH and it allowed the accurate control of the media pH by the automatic addition of acid or alkali. pH 7.5 cells were grown in normal flask batch culture. The cell number, cell volume, and chlorophyll content of both algae were determined over a wide range of pH values, showing that differences in external pH had significant effects on individual cells. Protein concentrations were measured and were shown to increase in pH 9.0 grown cells. Determination of cell volume, internal pH and membrane potential have been carried out using radiolabelled isotopes for algae grown over a wide pH range. Cell volume was shown to increase at both acid and alkaline pH values. The internal pH of both algae was found to be at a more neutral pH than the external pH. For both D. parva and C submarinum, the membrane potential increased with increasing external pH. Enzyme activities in crude extracts were measured to establish the effects of external pH changes on metabolic pathways. The activity of these enzymes, taken from different organelles in the cell, was used to investigate the uniformity of internal pH
Photonic porous silicon as a pH sensor
No full textChronic wounds do not heal within 3 months, and during the lengthy healing process, the wound is invariably exposed to bacteria, which can colonize the wound bed and form biofilms. This alters the wound metabolism and brings about a change of pH. In this work, porous silicon photonic films were coated with the pH-responsive polymer poly(2-diethylaminoethyl acrylate). We demonstrated that the pH-responsive polymer deposited on the surface of the photonic film acts as a barrier to prevent water from penetrating inside the porous matrix at neutral pH. Moreover, the device demonstrated optical pH sensing capability visible by the unaided eye
Control of mineral scaling in power plant recirculating cooling systems using treated municipal wastewater
No full textThe global energy demand is projected to increase by 77% from 2006 to 2030 along with a projected 38% increase in freshwater withdrawal for cooling in power industry. Finding alternative sources of water for cooling has become essential for future energy generation in thermoelectric power plants because of water scarcity in many parts of the US. Treated municipal wastewater is considered as one of the most promising alternative water sources because of its geographic distribution and abundant quantity. However, its impaired water quality makes the cooling tower management more challenging. Therefore, effective approaches are required to prevent scaling, corrosion, and biological growth to promote the reuse of treated municipal wastewater as cooling water in power plants.
This study focuses on understanding mineral scale formation and developing effective mitigation methods when using tertiary treated municipal wastewater as power plant cooling makeup. Two types of tertiary-treated municipal wastewater that were evaluated included secondary-treated water with pH adjustment (MWW_pH) and water from secondary-treatment followed by nitrification and sand filtration (MWW_NF). Laboratory-scale studies and pilot-scale cooling systems were used to evaluate mineral scaling formation and inhibition on non-heated surfaces (e.g., pipelines, tower packing, etc.) under conditions relevant to full-scale cooling systems. Results showed that pH adjustment to 7.8 plus the addition of 5 ppm polymaleic acid (PMA) could reduce the scaling significantly with MWW_pH. MWW_NF exhibited little scaling potential, which is related in part to the lower pH and alkalinity in this water. Amorphous calcium phosphate (ACP) was the primary form of mineral scale on non-heated surface with the above two-types of tertiary-treated municipal wastewater.
A bench-scale experimental system was designed to simulate the condenser surface to study the impacts of mineral scaling on the heated surfaces and the effectiveness of proposed scaling control strategies under these conditions. Heated surface favored the formation of hydroxyapatite (HAP), the most thermodynamically stable calcium phosphate, was the main reason for the crystalline fouling with MWW_pH at pH 7.8. 10 ppm PMA addition could suppress the crystalline fouling of MWW_pH at 7.8 to a low level by inhibiting the transformation of amorphous calcium phosphate to hydroxyapatite during the test period. Significant crystalline fouling was identified with MWW_NF at pH 7.2 while pH adjustment to 7.8 resulted in negligible fouling.
The impact of flow velocity on particle deposition was analyzed in a quantitative model, showing positive deposition potential for bulk precipitates at flow velocity of 0.5 and 0.4 m/s while little particulate fouling was theoretically predicted at 0.6 m/s in the test situation. Bench-scale studies were consistent the model prediction, confirming that the model could be used to identify optimal hydrodynamic conditions to control depositions of bulk precipitates.
The mechanism of calcium phosphate scale control by common antiscalants included PMA and 1-hydroxyethane 1,1-diphosphonic acid (HEDP) was elucidated to provide scientific background for the effective scaling mitigation when treated municipal wastewater is used as make-up in thermoelectric power plant cooling systems. Both PMA and HEDP inhibited the transformation of ACP to HAP by preventing the aggregation of ACP particles. However, PMA dispersed the ACP particles mainly through electrostatic repulsive force while hydration force was hypothesized to be the reason for the function of HEDP in dispersion.
The key findings of this study indicate that it is possible to control mineral scaling through direct chemical addition at proper operating conditions when treated municipal wastewater is used as makeup water in the recirculating cooling system. This study not only evaluated scaling control methods in cooling systems, but also revealed the fundamentals of scaling formation and inhibition
Open charm tetraquarks in broken SU(3)_F symmetry
No full textPrompted by a recent lattice QCD calculation, we review the SU(3) light quark flavor structure of charmed tetraquarks with spin 0 diquarks. Fermi statistics forces the three light quarks to be in the representation 3¯⊗3¯=3⊕6¯. This agrees with the weak repulsion in the 15 of the 3⊗8 in D¯K scattering studied on the lattice. We analyze the 3⊕6¯ multiplet broken by the strange quark mass and determine the five independent masses from the known masses of diquarks. The mass of Ds0*(2317) is predicted within 50 MeV accuracy. The recently observed D¯s--(2900) and D¯s0(2900), likely part of a I=1 multiplet, with flavor composition c¯q¯q′s, and X0(2900), an isosinglet with flavor composition c¯s¯ud, fit naturally in a 3⊕6¯ structure as the first radial excitations. We discuss also the decay modes of Ds0*(2317), of the radial excitations and of the predicted particles.Prompted by a recent lattice QCD calculation, we review the SU(3) light quark flavor structure of charmed tetraquarks with spin-0 diquarks. Fermi statistics forces the three light quarks to be in the representation 3*x3*= 3+6*. This agrees with the weak repulsion in the 15 of the 3x8 in Dbar K scattering studied on the lattice. We analyze the 3+6* multiplet broken by the strange quark mass and determine the five independent masses from the known masses of diquarks. The mass of D^* _{s0}(2317) is predicted within 50 MeV accuracy. The recently observed D_s^{--}(2900) and D_s^0(2900), likely part of a I=1 multiplet, with flavor composition c* q* q' s and X_0(2900), an isosinglet with flavor composition c*s* ud, fit naturally in a 3+6* structure as the first radial excitations. We discuss also the decay modes of D^* _{s0}(2317), of the radial excitations and of the predicted particles
Toward Inclusive, Evidence-Based rTMS Care for Patients With Co-Occurring Substance Use Disorders
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
pH-dependent behavior of RIP2CARD.
No full textA—Overlay of the region of 13C-CT-HSQC spectra of RIP2CARD, containing the cross-peaks from the Arg and Lys sidechains, recorded at pH 3.3 (blue), 3.7 (red) and 4.4 (magenta). Assignment of signals is indicated, asterisks denote the folded cross-peaks from the CαH moieties. B—structure of RIP2CARD with highlighted charged sidechains, taking part in the salt bridges.C—concentration of monomeric RIP2CARD (the relative intensity of W438 sidechain cross-peak in HSQC) is plotted as a function of ambient pH for 300 μM sample without salt (blue circles), 100 μM sample without salt (magenta circles) and 100 μM sample with 50 mM NaCl (blue circles). Solid and dashed dark blue lines denote the net charge and charge of the polyhistidine tag, calculated based on the measured pKa magnitudes. D—measured pKa of Glu, Asp sidechains and C-terminal residue of RIP2CARD. Red bars denote the sidechains which are engaged in salt bridges.</p
An extracellular steric seeding mechanism for Eph-ephrin signaling platform assembly
No full textErythropoetin-producing hepatoma (Eph) receptors are cell-surface protein tyrosine kinases mediating cell-cell communication. Upon activation, they form signaling clusters. We report crystal structures of the full ectodomain of human EphA2 (eEphA2) both alone and in complex with the receptor-binding domain of the ligand ephrinA5 (ephrinA5 RBD). Unliganded eEphA2 forms linear arrays of staggered parallel receptors involving two patches of residues conserved across A-class Ephs. eEphA2-ephrinA5 RBD forms a more elaborate assembly, whose interfaces include the same conserved regions on eEphA2, but rearranged to accommodate ephrinA5 RBD. Cell-surface expression of mutant EphA2s showed that these interfaces are critical for localization at cell-cell contacts and activation-dependent degradation. Our results suggest a 'nucleation' mechanism whereby a limited number of ligand-receptor interactions 'seed' an arrangement of receptors which can propagate into extended signaling arrays
Vitamin D and innate immunity in pneumonia and COPD
No full textA resurgence of interest in vitamin D research has led to the discovery that it plays a role in an unexpectedly large number of biological processes, and that reduced levels of this hormone are implicated in a range of diseases. In fact, it is estimated that vitamin D is involved in the regulation of 3% of the human genome. Two genes containing the target sequence indicative of vitamin D regulation are those encoding LL-37 and hBD-2. These antimicrobial peptides are integral components of the innate immune system and act as natural antibiotics to help combat infection.
The respiratory epithelium exposes a large surface area to environmental pathogens, making the innate immune response extremely important in its defence. Microbial infection of the respiratory tract is the cause of pneumonia, and is implicated in cases of COPD exacerbation. This study aimed to determine whether a relationship existed between vitamin D, LL-37 and hBD-2 in 185 patients admitted to Waikato hospital with either condition. It was hypothesised that low vitamin D would correlate with reduced peptide levels, and that this would be associated with increased infection severity and higher mortality rates.
Peptide concentrations in patient plasma were measured by indirect ELISA and compared to 25D levels. Statistical analysis revealed no significant associations between vitamin D status, peptide levels and severity, but did show increased mortality in individuals with severe vitamin D deficiency or low LL-37.
Based on the significance of LL-37 as a predictor of mortality (particularly in COPD), development of a plasma screening method using MALDI-TOF mass spectrometry was attempted, as a potential means of identifying patients most at risk. The success of this method was limited however, as the low abundance and small size of the mature peptide caused detection problems.
A protocol for assessing the vitamin D binding protein (DBP) genotype was developed, as it influences baseline 25D levels and response to supplementation. The association between low vitamin D and mortality suggests that supplementation could improve survival rates and, as the supplement dose required for effectiveness is genotype-dependent, this method could allow determination of the appropriate amount to administer to at-risk individuals
An intracellular pH gradient in the anammox bacterium Kuenenia stuttgartiensis as evaluated by (31)P NMR
No full textThe cytoplasm of anaerobic ammonium oxidizing (anammox) bacteria consists of three compartments separated by membranes. It has been suggested that a proton motive force may be generated over the membrane of the innermost compartment, the “anammoxosome”. 31P nuclear magnetic resonance (NMR) spectroscopy was employed to investigate intracellular pH differences in the anammox bacterium Kuenenia stuttgartiensis. With in vivo NMR, spectra were recorded of active, highly concentrated suspensions of K. stuttgartiensis in a wide-bore NMR tube. At different external pH values, two stable and distinct phosphate peaks were apparent in the recorded spectra. These peaks were equivalent with pH values of 7.3 and 6.3 and suggested the presence of a proton motive force over an intracytoplasmic membrane in K.stuttgartiensis. This study provides for the second time—after discovery of acidocalcisome-like compartments in Agrobacterium tumefaciens—evidence for an intracytoplasmic pH gradient in a chemotrophic prokaryotic cell.BiotechnologyApplied Science
- …
