Phi Values Research Articles

Effect of ammonium groups of sulfonated polysulfone membrane on its pervaporation performance

Ammonium-exchanged membranes were prepared and utilized for the dehydration of ethanol/water mixtures by pervaporation. This paper presents an original investigation on the influence of the ammonium content on the hydrophilic and swelling properties of ion-exchange membranes. The identification of ammonium was carried out by infrared ray (IR) spectroscopy. It was found that the content of ammonium did not significantly change the membrane surface morphology but considerably decreased the water contact angle for the membranes. The optimum ammonium substitution in the membrane resulted in a high pervaporation performance for the dehydration of ethanol solution. More than 99% of permeate water was obtained in the pervaporation process. Based on the sorption and diffusion mechanism discussion, the high selectivity of water to ethanol was mainly contributed by the diffusion rate difference of permeants in the membrane rather than the sorption. The hydrophilicity improvement and decrease in swelling of modified membranes contributed to the high selectivity of ion-exchanged membranes for pervaporation. An excellent dehydration performance of ion-exchanged membranes was observed. All the PSI values of the ion-exchanged membrane were higher than 10 5, which could be attributed to the suitable conditions applied for preparing ion-exchanged polysulfone membranes.

Convection in nanofluids with a particle-concentration-dependent thermal conductivity

Thermal convection in nanofluids is investigated by means of a continuum model for binary-fluid mixtures, with a thermal conductivity depending on the local concentration of colloidal particles. The applied temperature difference between the upper and the lower boundary leads via the Soret effect to a variation of the colloid concentration and, therefore, to a spatially varying heat conductivity. An increasing difference between the heat conductivity of the mixture near the colder and the warmer boundary results in a shift of the onset of convection to higher values of the Rayleigh number for positive values of the separation ratio ψ>0 and to smaller values in the range ψ<0. Beyond some critical difference of the thermal conductivity between the two boundaries, we find an oscillatory onset of convection not only for ψ<0, but also within a finite range of ψ>0. This range can be extended by increasing the difference in the thermal conductivity, and it is bounded by two codimension-2 bifurcations.

The angle of internal flow as an indicator of filling and drug release properties of capsule formulations.

The cohesiveness of size fractions of acetylsalicylic acid and lactose alone and in various combinations has been determined by estimation of the rate of decrease in volume as a function of tamping under standard conditions. The cohesiveness was quantified in terms of empirically derived characteristic, the angle of internal flow phi. The value of phi was found to decrease with the particle size of acetylsalicylic acid, but not lactose, and was found to be dependent on the relative proportion and particle sizes of acetylsalicylic acid and lactose when blends of powder were studied. The value of the time for 50% of the drug content to be released from a hard gelatin capsule in an in-vitro dissolution test, T50, was found to decrease with decreasing values of omega for capsules containing acetylsalicylic acid alone. For capsules containing powder blends there was no consistent relationship between the value of T50 and phi.

Differentiation of prostate cancer from benign lesions using strain index of transrectal real-time tissue elastography

This study was to assess the diagnostic value of strain index (SI) for transrectal real-time tissue elastography (TRTE) on differentiating malignant from benign lesions in the prostate peripheral zone. 83 patients suspected of having prostate cancer (PCa) underwent transrectal ultrasonography (TRUS) and TRTE examinations. The lesions in the prostate peripheral zone detected by TRTE were set as the regions of interest (ROI) for strain ratio (SR) measurement (SRA). The moderate texture tissues without lesion were set as the reference ROI for SR measurement (SRB). Then, SI (SRB/SRA) of total lesions (ASI) and local lesion (PSI) were calculated, and the diagnostic values of ASI and PSI on differentiating benign from malignant lesions were assessed respectively. The range of PSI was 2.23-67.21 (29.97 ± 15.58) in malignant tumors and 0. 4-43.6 (7.79 ± 8.75) in benign lesions (AUC=0.90), while the range of ASI was 2.84-47.9 (8.38 ± 12.20) in malignant tumors and 0.4 -2.79 (5.85 ± 7.29) in benign lesions (AUC=0.62). There was significant difference of PSI values between the benign and malignant lesions (P<0.01). At the cutoff value of 17.44, PSI yielded the highest sensitivity (74.5%) and specificity (83.3%) for discriminating PCa from benign lesions. The capability of PSI in the diagnosis of PCa improved with the increase of Gleason scores. PSI is one of the elasticity parameters obtained easily by TRTE, it can provide more information in the differentiation of prostate peripheral zone lesions.

Energy Changes at the Acetylcholine Receptor Gate Region

Abstract The neuromuscular acetylcholine receptor (AChR) alternatively switches between an inactive (closed) and active (open) conformation. during the gating isomerization (R↔R∗) process. The ‘gate’ region is formed by the equatorial residues (9’-16’). We and others have speculated that channel gating involves a wetting/de-wetting of this region of the pore, based on measurements of gating equilibrium changes caused by mutations, phi value analysis and molecular dynamics simulations. We are studying the coupling energies between 9’-13’ residues in different subunits, by estimating the effect of mutations, separately vs. in combination, on the unliganded gating equilibrium constant E0. The end states and conformational pathway for AChR gating is fundamentally the same with and without agonists, and E0 can be estimated without obfuscation by channel block. We characterized two background mutants (αA96N/W149S and αA96H/Y96H) that greatly increase spontaneous gating and exhibit simple two-state kinetics (E0 = 0.076 and 0.031). These E0 values predict an E0wt value that is similiar to previous estimates (∼6.5x10−7). With these spontaneously-opening backgrounds, the individual free energy changes for βV13A and δV13'L (−4.1 kcal/mol and −1.9 kcal/mol) are similar to previous estimates obtained by using diliganded AChRs. Initial results suggest that these 13’ mutants are only weakly coupled (∼-1.2 kcal/mol). We expect these studies will help unravel the structural changes in protein and water that occur at the AChR gate region.

Metabolic insights into the yeast response to propionic acid based on high resolution 1H NMR spectroscopy

The experimental model Saccharomyces cerevisiae has been widely used to elucidate the molecular mechanisms behind resistance to weak acids in fungi, an essential knowledge for the development of more suitable preservation strategies. Previous studies, based on transcriptomic and chemogenomic approaches, revealed a number of yeast responses to propionic acid, widely used in the preservation of bakery and fresh dairy products. In the present work we report the metabolic changes occurring during yeast adaptation to, and growth in, the presence of this weak acid (20 mM at pH 4) using high resolution 1H NMR spectroscopy coupled with multivariate statistical analysis. The metabolic profiles highlighted the separation of propionic acid-induced lag-phase in two parts. The initial period of incubation under acid stress (up to 3 h following the inoculation of an unadapted yeast population) was characterized by a decrease of cell viability and of the average intracellular pH (pHi) values. The final part of this incubation period (from 4 to 6 h of incubation) was characterized by the start of cell division in the presence of the acid, an increase of the average pHi and a metabolic profile close to the profile exhibited by cells in the exponential phase of growth in propionic acid supplemented medium. An association between the average pHi values and the levels of glutamate and propionate during growth latency was identified. Changes in the cell content in other amino acids, ATP, NAD+, glycerol and trehalose were also registered during yeast incubation with propionic acid. These alterations are discussed in the context of the global response to this weak acid.

Automated detection of left ventricular dyskinesis by gated blood pool SPECT

The ability to detect left ventricular (LV) apical dyskinesis, the hallmark of an aneurysm, is an important requirement of diagnostic cardiac imaging modalities that perform wall motion analysis. Our investigation assessed the ability of gated blood pool single-photon emission-computed tomography (GBPS) to automatically detect LV dyskinesis, using cardiac magnetic resonance (CMR) as the reference standard. GBPS data were analyzed for 41 patients with congestive heart failure or cardiomyopathy and compared with ECG-gated TrueFISP CMR evaluations. An experienced nuclear cardiologist without the knowledge of quantitative GBPS or CMR results graded visual impressions of regional wall motion while examining cinematic playbacks of GBPS images. GBPS algorithms automatically isolated LV counts and computed regional phase (phi) values in each of 17 conventional American Heart Association LV segments. LV asynchrony was quantified by the two local measures: maximum apical phi difference (Deltaalpha), and standard deviation among apical phases (sigmaalpha), and by the five global measures: varphi histogram bandwidth (BWHistogram), phi histogram standard deviation (sigmaHistogram), Z-scores, Entropy, and Synchrony. For CMR data, an expert manually drew endocardial LV outlines to measure regional wall motion in 17 LV segments. Apical dyskinesis was present in nine patients. Among GBPS measurements, the method with the greatest accuracy for detecting dyskinesis was Deltaalpha (receiver operating characteristic area=95%). The only method with a sufficiently high kappa statistic to represent 'very good agreement' with CMR was Deltaalpha, with kappa=0.81. Deltaalpha was more sensitive in detecting dyskinesis than visual analysis (100 vs. 33%, P=0.01). Automatic GBPS computations accurately identified patients with LV dyskinesis, and detected dyskinesis more successfully than did visual analysis.

Na+-dependent HCO3− Import by the slc4a10 Gene Product Involves Cl− Export

The slc4a10 gene encodes an electroneutral Na(+)-dependent HCO(3)(-) importer for which the precise mode of action remains unsettled. To resolve this issue, intracellular pH (pH(i)) recordings were performed upon acidification in the presence of CO(2)/HCO(3)(-) by 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) fluorometry of stably slc4a10-transfected NIH-3T3 fibroblasts. slc4a10 expression induced a significant Na(+)-dependent pH(i) recovery, which was accompanied by an increase in the intracellular Na(+) concentration evaluated by use of the Na(+)-sensitive fluorophore CoroNa Green. The estimated Na(+):HCO(3)(-) stoichiometry was 1:2. Cl(-) is most likely the counterion maintaining electroneutrality because (i) Na(+)-dependent pH(i) recovery was eliminated in Cl(-)-depleted cells; (ii) acute extracellular Cl(-) removal led to a larger alkalization in slc4a10-transfected cells than in control cells; and (iii) the 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid (DIDS)-sensitive and Na(+)- and HCO(3)(-)-dependent (36)Cl(-)-efflux during pH(i) recovery was significantly greater in acidified slc4a10-transfected cells than in control cells. Charged amino acids specific to slc4a gene family members that transport Na(+) and are expected to move more HCO(3)(-) molecules/turnover were targeted by site-directed mutagenesis. Na(+)-dependent pH(i) recovery was reduced in each of the single amino acid mutated cell lines (E890A, E892A, H976L, and H980G) compared with wild type slc4a10-transfected cells and completely eliminated in quadruple mutant cells. In conclusion, the data suggest that slc4a10 expressed in mammalian cells encodes a Na(+)-dependent Cl(-)/HCO(3)(-) exchanger in which four specific charged amino acids seem necessary for ion transport.

Tattoo inks contain polycyclic aromatic hydrocarbons that additionally generate deleterious singlet oxygen

In the past years, tattoos have become very popular worldwide, and millions of people have tattoos with mainly black colours. Black tattoo inks are usually based on soot, are not regulated and may contain hazardous polycyclic aromatic hydrocarbons (PAHs). Part of PAHs possibly stay lifelong in skin, absorb UV radiation and generate singlet oxygen, which may affect skin integrity. Therefore, we analysed 19 commercially available tattoo inks using HPLC and mass spectrometry. The total concentrations of PAHs in the different inks ranged from 0.14 to 201 microg/g tattoo ink. Benz(a)pyrene was found in four ink samples at a mean concentration of 0.3 +/- 0.2 microg/g. We also found high concentrations of phenol ranging from 0.2 to 385 microg/g tattoo ink. PAHs partly show high quantum yields of singlet oxygen (Phi(Delta)) in the range from 0.18 to 0.85. We incubated keratinocytes with extracts of different inks. Subsequent UVA irradiation decreased the mitochondrial activity of cells when the extracts contained PAHs, which sufficiently absorb UVA and show simultaneously high Phi(Delta) value. Tattooing with black inks entails an injection of substantial amounts of phenol and PAHs into skin. Most of these PAHs are carcinogenic and may additionally generate deleterious singlet oxygen inside the dermis when skin is exposed to UVA (e.g. solar radiation).

Solution conformation of a tetradecapeptide stabilized by two di‐n‐propyl glycine residues

The solution conformation of a designed tetradecapeptide Boc-Val-Ala-Leu-Dpg-Val-Ala-Leu-Val-Ala-Leu-Dpg-Val-Ala-Leu-OMe (Dpg-14) containing two di-n-propyl glycine (Dpg) residues has been investigated by (1)H NMR and circular dichroism in organic solvents. The peptide aggregates formed at a concentration of 3 mM in the apolar solvent CDCl(3) were broken by the addition of 12% v/v of the more polar solvent DMSO-d(6). Successive N(i)H <--> N(i+1)H NOEs observed over the entire length of the sequence in this solvent mixture together with the observation of several characteristic medium-range NOEs support a major population of continuous helical conformations for Dpg-14. Majority of the observed coupling constants (3)JNHC(alpha)H) also support phi values in the helical conformation. Circular dichroism spectra recorded in methanol and propan-2-ol give further support in favor of helical conformation for Dpg-14 and the stability of the helix at higher temperature.

An Exploratory Study of Determinants and Corrective Measures for Software Piracy and Counterfeiting in the Digital Age

Software piracy and counterfeiting is a global problem that has resulted in huge economic losses worldwide. This paper proposes a theory-based approach to study the key factors contributing to piracy and counterfeiting issues. We first developed a theoretical model linking the antecedents into the key factors using information acquired from an extended literature review. We then undertook a survey of thirty business professionals representing different industries, functional roles and different levels of work exposure to software usages in Singapore to investigate the issues. Specifically, the objectives of the survey were to: (1) investigate the key issues associated to software piracy and counterfeiting; (2) identify the factors that have contributed to the software piracy and counterfeiting; and (3) draw up a refined list of appropriate measures to counter software piracy and counterfeiting. Through the structural use of Non-Parametric Correlation Test, Chi-Square Test for Independence, Fisher Exact Probability Test and Phi value, our findings showed that the lack of awareness to software usage laws and regulations, the perceived lack of enforcement measures and penalties, and the lack of educational programs catering to the proper usage of software were the key factors contributing to the software piracy and counterfeiting issues. The findings are useful to managers of software companies and policy-makers in reviewing existing software protection policies, laws and regulations, such that any flaws or loopholes can be

Convection in colloidal suspensions with particle-concentration-dependent viscosity

The onset of thermal convection in a horizontal layer of a colloidal suspension is investigated in terms of a continuum model for binary-fluid mixtures where the viscosity depends on the local concentration of colloidal particles. With an increasing difference between the viscosity at the warmer and the colder boundary the threshold of convection is reduced in the range of positive values of the separation ratio psi with the onset of stationary convection as well as in the range of negative values of psi with an oscillatory Hopf bifurcation. Additionally the convection rolls are shifted downwards with respect to the center of the horizontal layer for stationary convection psi>0 and upwards for the Hopf bifurcation (psi<0.

THE CHARACTERISTIC CHANGES OF PROTEASE CG-10 IMMOBILIZED BY BENTONITE

The CG-10 isolate is a thermophile microorganism live in extreme environments, a hot spring located at Cangar East Java, having temperature 50 oC. The isolate had following characteristics: rod shaped cells, gram-positive, size of cells 6-14 µm, aerobic, and obligate thermophile. Based on the nucleotide sequences of its 16S-rRNA gene indicated that these isolate was closely related to Bacillus caldoxylolyticus (98.305% sequence similarity). The enzymes produced by thermophile microorganism were usually active at a higher temperature than that of the environment in which they live. Therefore it is possible to use this enzyme in industries requiring high temperature in their production processes. The CG-10 isolate grew well in a liquid waste of tofu and could secretion extracellular protease. The protease was isolated by fractioning at 35% (w/v) ammonium sulfate, centrifuged at 4000 rpm for 15 minutes, and had the following characteristics: optimum temperature 80 oC, optimum pH 8, the molecular weight 53.000-76.000 Dalton (for the protease showing the highest activity), pHI value between 7.5 up to 8.2, and could be classified as a serine alkaline protease. For increasing the efficiency of this protease in industries had been done by immobilization with bentonite. The immobilization process is done at optimum pH (pH 5). The characteristic changes research of protease CG-10 isolate immobilized by bentonite had been done. The immobile enzyme showed different characteristics for that of the native (mobile enzymes). The immobile enzyme showed a different optimum temperature, a higher heat resistance but the same optimum pH as the native enzyme. Keywords: Bacillus caldoxylolyticus, protease, immobilization

Characterization of the Excited States of Indigo Derivatives in their Reduced Forms

A comprehensive characterization of the electronic spectral and photophysical properties of the leuco (reduced) form of several indigo derivatives, including indigo and Tyrian Purple, with di-, tetra-, and hexa-substitution, was obtained in solution. The characterization involves absorption, fluorescence, and triplet-triplet absorption spectra, together with quantitative measurements of quantum yields of fluorescence, phi(F) (0.46-0.04), intersystem crossing, phi(Tau) (0.013-0.034), internal conversion, phi(IC), and the corresponding lifetimes. The position and degree of substitution promote differences in the spectral and photophysical properties displayed by the investigated leuco derivatives. The phi(F) values are about two orders of magnitude higher than those previously obtained for the corresponding keto forms. Also in contrast with the behavior found for the keto forms, the S(1) approximately approximately -->T(1) intersystem crossing is an efficient route for the excited-state deactivation channel. These findings strengthen the fact that, in contrast to keto indigo where the internal conversion dominates the deactivation of the excited-state, with leuco indigo (and derivatives), the excited state deactivation involves competition between internal conversion, triplet state formation, and fluorescence. A time-resolved investigation of one of the compounds in glycerol showed the presence of a photoisomerization process.

Low-energy-threshold analysis of the Phase I and Phase II data sets of the Sudbury Neutrino Observatory

Results are reported from a joint analysis of Phase I and Phase II data from the Sudbury Neutrino Observatory. The effective electron kinetic energy threshold used is T_eff=3.5 MeV, the lowest analysis threshold yet achieved with water Cherenkov detector data. In units of 10^6 cm^{-2} s^{-1}, the total flux of active-flavor neutrinos from 8B decay in the Sun measured using the neutral current (NC) reaction of neutrinos on deuterons, with no constraint on the 8B neutrino energy spectrum, is found to be Phi_NC = 5.140 ^{+0.160}_{-0.158} (stat) ^{+0.132}_{-0.117} (syst). These uncertainties are more than a factor of two smaller than previously published results. Also presented are the spectra of recoil electrons from the charged current reaction of neutrinos on deuterons and the elastic scattering of electrons. A fit to the SNO data in which the free parameters directly describe the total 8B neutrino flux and the energy-dependent nu_e survival probability provides a measure of the total 8B neutrino flux Phi_8B = 5.046 ^{+0.159}_{-0.152} (stat) ^{+0.107}_{-0.123} (syst). Combining these new results with results of all other solar experiments and the KamLAND reactor experiment yields best-fit values of the mixing parameters of theta_{12}=34.06 ^{+1.16}_{-0.84} degrees and Delta m^2_{21}=7.59 ^{+0.20}_{-0.21} x 10^{-5} eV^2. The global value of Phi_8B is extracted to a precision of ^{+2.38}_{-2.95} %. In a three-flavor analysis the best fit value of sin^2\theta_{13} is 2.00 ^{+2.09}_{-1.63} x 10^{-2}. Interpreting this as a limit implies an upper bound of sin^2\theta_{13} < 0.057 (95% C. L.).

Population Structure as Revealed by mtDNA and Microsatellites in Northern Fur Seals, Callorhinus ursinus, throughout Their Range

BackgroundThe northern fur seal (Callorhinus ursinus; NFS) is a widely distributed pinniped that has been shown to exhibit a high degree of philopatry to islands, breeding areas on an island, and even to specific segments of breeding areas. This level of philopatry could conceivably lead to highly genetically divergent populations. However, northern fur seals have the potential for dispersal across large distances and have experienced repeated rapid population expansions following glacial retreat and the more recent cessation of intensive harvest pressure.Methodology/Principal FindingsUsing microsatellite and mitochondrial loci, we examined population structure in NFS throughout their range. We found only weak population genetic structure among breeding islands including significant FST and ΦST values between eastern and western Pacific islands.ConclusionsWe conclude that insufficient time since rapid population expansion events (both post glacial and following the cessation of intense harvest pressure) mixed with low levels of contemporary migration have resulted in an absence of genetic structure across the entire northern fur seal range.

Structural determinants stabilizing helical distortions related to proline

The distortions related to proline in a alpha-helix can be accommodated by different structural elements. To obtain an exhaustive view of these distortions, we data mined a non-redundant subset of the Protein Data Bank in search of proline residues included either within contiguous helices or within structural motifs in which two helices are joined by a few linker residues with backbone dihedral angles in the generous alpha region. The distortions correspond to "typical" and "non-typical" proline distortions, with relative ratio of 0.65 and 0.35, respectively. Analysis of "non-typical" proline distortions indicates that most linkers have one (75%) or two residues (20%) and that proline is preferentially located at the second or third position of the second helix (95%). The dihedral angles of the linker residues are located in two areas of the generous alpha region. Structures with linker(s) in the alpha1 area, which is characterized by very negative phi values, possess i to i-5 H-bonds and correspond to pi bulges. Structures with linker(s) in the alpha2 area, which links the alpha and beta regions, possess i to i-3 H-bonds and correspond to tight turns. Further classification of bulges and turns as a function of the linker length and proline position yields five canonical structures, representing 85% of "non-typical" proline distortions. These structures are characterized by distinct H-bonding patterns and structural determinants and correspond to different classes of pi bulges and tight turns. This hierarchical approach provides a straightforward and robust classification of proline-related helical distortions.

Separate Gating Mechanisms Mediate the Regulation of K2P Potassium Channel TASK-2 by Intra- and Extracellular pH

TASK-2 (KCNK5 or K(2P)5.1) is a background K(+) channel that is opened by extracellular alkalinization and plays a role in renal bicarbonate reabsorption and central chemoreception. Here, we demonstrate that in addition to its regulation by extracellular protons (pH(o)) TASK-2 is gated open by intracellular alkalinization. The following pieces of evidence suggest that the gating process controlled by intracellular pH (pH(i)) is independent from that under the command of pH(o). It was not possible to overcome closure by extracellular acidification by means of intracellular alkalinization. The mutant TASK-2-R224A that lacks sensitivity to pH(o) had normal pH(i)-dependent gating. Increasing extracellular K(+) concentration acid shifts pH(o) activity curve of TASK-2 yet did not affect pH(i) gating of TASK-2. pH(o) modulation of TASK-2 is voltage-dependent, whereas pH(i) gating was not altered by membrane potential. These results suggest that pH(o), which controls a selectivity filter external gate, and pH(i) act at different gating processes to open and close TASK-2 channels. We speculate that pH(i) regulates an inner gate. We demonstrate that neutralization of a lysine residue (Lys(245)) located at the C-terminal end of transmembrane domain 4 by mutation to alanine abolishes gating by pH(i). We postulate that this lysine acts as an intracellular pH sensor as its mutation to histidine acid-shifts the pH(i)-dependence curve of TASK-2 as expected from its lower pK(a). We conclude that intracellular pH, together with pH(o), is a critical determinant of TASK-2 activity and therefore of its physiological function.

Dependence of Photochemical Reactivity of the All‐trans Retinal Protonated Schiff Base on the Solvent and the Excitation Wavelength

An all-optical experimental technique aimed at measuring photoisomerization quantum yield (phi) of the all-trans protonated Schiff base of retinal in solution has been implemented. Upon the increase in the excitation wavelength from 400 to 540 nm a slight increase in phi from 0.16 +/- 0.03 to 0.20 +/- 0.02 is observed in the chromophore dissolved in methanol, whereas the phi value of the one dissolved in acetonitrile varies only from 0.22 +/- 0.03 (400 nm) to 0.23 +/- 0.04 (540 nm). The results suggest that dissipation of the excited-state vibrational energy excess, along with environment-induced modifications of the potential energy surfaces are necessary for an efficient retinal photoisomerization in both solvent and protein environment.

Detection of SNP-QTL associated with pork pHI and pHU value

Pork pH value is an important trait related to meat quality, the trial has screened the SNP-QTL associated with pork pHI and pHU from genome wide SNP screening in a Danish swine predgree. The result indicated there was a QTL on chromosome 6 which was associated with pork pHI and pHU value signficiantly. Effect value of QTL associated with pHI significantly was between 2.6%~8.5%, FLJ30670 locus had a strong effect on pHI and it took 8.5% of total variation, while effect value of QTL associated with pHU significantly was 2.1%~4.3%, all of which were lower than pHI related effect of them, the FUT1 locus had a strongest effect on pHU and it took the 4.3% of total variation, indicating acidity of pork within 24 h was more likely to be affected by other environmental factors.