Lack Of Temperature Dependence Research Articles

Impact of temperature dependence on the possible contribution of organics to new particle formation in the atmosphere

Abstract. Secondary particles formed via new particle formation (NPF) dominate cloud condensation nuclei (CCN) abundance in most parts of the troposphere and are important for aerosol indirect radiative forcing (IRF). Laboratory measurements have shown that certain organic compounds can significantly enhance the binary nucleation of sulfuric acid and H2O. According to our recent study comparing particle size distributions measured in nine forest areas in North America with those predicted by a global size-resolved aerosol model, current H2SO4–organics nucleation parameterizations appear to significantly overpredict NPF and particle number concentrations in summer. The lack of temperature dependence in the current H2SO4–organics nucleation parameterization has been suggested to be a possible reason for the observed overprediction. In this work, H2SO4–organics clustering thermodynamics from quantum chemical studies has been employed to develop a scheme to incorporate temperature dependence into H2SO4–organics nucleation parameterization. We show that temperature has a strong impact on H2SO4–organics nucleation rates and may reduce the nucleation rate by ∼ 1 order of magnitude per 10 K of temperature increase. The particle number concentrations in summer over North America based on the revised scheme is a factor of more than 2 lower, which is in much better agreement with the observations. With the temperature-dependent H2SO4–organics nucleation parameterization, the summer CCN concentrations in the lower troposphere in the Northern Hemisphere are about 10–30 % lower compared to the temperature-independent parameterization. This study highlights the importance of the temperature effect and its impacts on NPF in the global modeling of aerosol number abundance.

NANO AND MICROPARTICLES of HfB<sub>2</sub>: THERMAL-EXPANSION COEFFICIENT AND ITS ANISOTROPY

The paper deals with the influence of a dimension factor on the thermal-expansion coefficient (TEC) of hafnium diboride. Nano-sized and microcrystalline hafnium diboride is investigated by method of X-ray diffraction in the temperature range of 300–1500 K. The size of nanocrystal HfB 2 with coherent scattering is 15 nanometers and remained constant during heating. The analysis of temperature dependence of the nano and microcrystalline HfB 2 parameters shows the non-linear growth of the cell metrics with increase in temperature. For the first time, the TEC of nano and microcrystalline HfB2 in the directions of crystallographic axes a and c are defined. The analytical expressions of temperature dependences of nano and microcrystalline HfB 2 of the cell parameters are received in the form of 2 degree polynomials. At the linear approximation of temperature dependence of the lattice parameters (i.e. at lack of temperature dependence of TEC), the TEC of microcrystalline HfB 2 in the studied temperature range are αa = 7.37 · 10 –6 and αс = 7.48 · 10 –6 K –1 for axes 0a and 0c respectively. The TEC of microcrystalline HfB 2 calculated according to X-ray diffraction data corresponds to TEC calculated by a dilatometric technique α = 7.49 · 10 –6 K –1 . At linear approximation of temperature dependence of the lattice parameters, the TEC of the nanocrystal HfB 2 are αa = 7.40 · 10 –6 and αс = 9.88 · 10 –6 K –1 for axes 0a and 0c respectively. The paper shows that the TEC of HfB 2 in nanocrystalline state is greater than the TEC of microcrystalline one. The difference between the TEC of nano and microcrystalline HfB2 are bound with increase in the surface energy of material with increase in dispersion. The paper finds the anisotropy of thermal expansion both micro and nanocrystal HfB 2 . The TEC on the axis 0c is higher than the TEC on the axis 0a. The anisotropy of TEC is explained taking into account the lengths and the nature of interconnections in crystalline structure of HfB 2 . The essential anisotropy of TEC in nanodimensional HfB 2 indicates the domination of the atomic fluctuations anharmonicity growth in nanocrystals in the direction of the axis 0c. The results obtained can be employed to create new environmentally friendly materials for the needs of alternative power engineering.

The noble effect of aging on the thermal conductivity of modified CNTs-ethylene glycol nanofluids

ABSTRACTIn order to improve the heat transfer process by using nanofluids, different nanoparticles and base fluids have been studied. In this work, stability and effect of aging and temperature on the thermal conductivity of CNTs-ethylene glycol (EG) nanofluids were investigated. Chemical functionalisation was used to oxidise the surface of CNTs. The functionalised CNTs were used to prepare the nanofluids by a two-step method. The stability of nanofluids was measured by UV-vis spectroscopy and the results showed that the nanofluids had a good stability over several days. Immediately after nanofluid preparation not too much increase was observed for thermal conductivity but the nanofluid aging had a great influence on the improvement of the thermal conductivity, as after 65 days, about 50% increase was observed. The increase has been attributed to forming an ordered nanolayer of EG molecules around the CNTs. Also no significant temperature dependence of thermal conductivity was observed up to 50°C possibly due to the lack of temperature dependence of CNTs Brownian motions.

Non-exponential Length Dependence of Conductance in Iodide-Terminated Oligothiophene Single-Molecule Tunneling Junctions.

An exponential decrease of molecular conductance with length has been observed in most molecular systems reported to date, and has been taken as a signature of non-resonant tunneling as the conduction mechanism. Surprisingly, the conductance of iodide-terminated oligothiophene molecules presented herein does not follow the simple exponential length dependence. The lack of temperature dependence in the conductance indicates that tunneling still dominates the conduction mechanism in the molecules. Transition voltage spectroscopy shows that the tunneling barrier of the oligothiophene decreases with length, but the decrease is insufficient to explain the non-exponential length dependence. X-ray photoelectron spectroscopy, stretching length measurement, and theoretical calculations show that the non-exponential length dependence is due to a transition in the binding geometry of the molecule to the electrodes in the molecular junctions as the length increases.

Neutral-current Hall effects in disordered graphene

A nonlocal Hall bar geometry is used to detect neutral-current Hall effects in graphene on silicon dioxide. Disorder is tuned by the addition of $\mathrm{Au}$ or $\mathrm{Ir}$ adatoms in ultrahigh vacuum. A reproducible neutral-current Hall effect is found in both as-fabricated and adatom-decorated graphene. The Hall angle exhibits a complex but reproducible dependence on gate voltage and disorder, and notably breaks electron-hole symmetry. An exponential dependence on length between Hall and inverse Hall probes indicates a neutral-current relaxation length of approximately $300\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$. The short relaxation length and lack of precession in a parallel magnetic field suggest that the neutral currents are valley currents. No signature of the spin-orbit coupling induced spin Hall effect is observed in the $\mathrm{Au}$- or $\mathrm{Ir}$-decorated graphene. The near lack of temperature dependence from 7 to 300 K is unprecedented among reports of valley Hall effect in graphene, and promising for using controlled disorder for room temperature neutral-current electronics.

Tuning of one-dimensional plasmons by Ag-Doping in Ag--ordered atomic wires

We generated arrays of silver wires with a height of 1 atom and an average width of 11 atoms on the Si(557) surface via self-assembly with local order, and investigated the 1D plasmon formation in them using a combination of high-resolution electron loss spectroscopy with low-energy electron diffraction. After a series of thermal desorption experiments followed by adding small concentrations of Ag, pure Ag- ordered arrays of nanowires, separated by (113) facets, are intrinsically semi metallic or semiconducting, i.e., the metallicity of the Ag wires seems to be caused by excess atoms added to the (locally) perfectly ordered layer. The proof has been carried out by post-adsorption of Ag atoms in the range between 0.004 to 0.03 monolayers and the quantitative determination of the frequency dependence of the 1D plasmon due to this excess Ag concentration. As expected for a doping mechanism, there is no minimum excess concentration. The lack of temperature dependence is not compatible with the formation of an adatom gas in the second layer, but suggests extrinsic doping by adatoms bound at the stepped (113) facets. Although strong deviations from a nearly free electron gas are expected in 1D, the Ag concentration dependence of the 1D plasmonic losses is fully compatible with the dependence predicted by this model. Adsorption of traces of residual gas can have a qualitatively similar doping effect.

A variable temperature spectroscopic study on Paracoccus pantotrophus pseudoazurin: Protein constraints on the blue Cu site

The blue or Type 1 (T1) copper site of Paracoccuspantotrophus pseudoazurin exhibits significant absorption intensity in both the 450 and 600 nm regions. These are sigma and pi S(Cys) to Cu(2+) charge transfer (CT) transitions. The temperature dependent absorption, EPR, and resonance Raman (rR) vibrations enhanced by these bands indicate that a single species is present at all temperatures. This contrasts the temperature dependent behavior of the T1 center in nitrite reductase [S. Ghosh, X. Xie, A. Dey, Y. Sun, C. Scholes, E. Solomon, Proc. Natl. Acad. Sci. 106 (2009) 4969-4974] which has a thioether ligand that is unconstrained by the protein. The lack of temperature dependence in the T1 site in pseudoazurin indicates the presence of a protein constraint similar to the blue Cu site in plastocyanin where the thioether ligand is constrained at 2.8 A. However, plastocyanin exhibits only pi CT. This spectral difference between pseudoazurin and plastocyanin reflects a coupled distortion of the site where the axial thioether in pseudoazurin is also constrained, but at a shorter Cu-S(Met) bond length. This leads to an increase in the Cu(2+)-S(Cys) bond length, and the site undergoes a partial tetragonal distortion in pseudoazurin. Thus, its ground state wavefunction has both sigma and pi character in the Cu(2+)-S(Cys) bond.

The effect of Al(OH) 4− on the dissolution rate of quartz

The influence of Al(OH) 4 − on the dissolution rate of quartz at pH 10–13 and 59–89 °C was determined using batch experiments. Al(OH) 4 − at concentrations below gibbsite solubility depressed the dissolution rate by as much as 85%, and this effect was greater at lower pH and higher Al(OH) 4 − concentration. Dissolution rates increased with increasing temperature; however, the percent decrease in rate due to the presence of Al(OH) 4 − was invariant with temperature for a given H + activity and Al(OH) 4 − concentration. These data, along with what is known about Al–Si interactions at high pH, are consistent with Al(OH) 4 − and Na + co-adsorbing on silanol sites and passivating the surrounding quartz surface. The observed pH dependence, and lack of temperature dependence, of inferred Al(OH) 4 − sorption also supports the assumption that the acid–base behavior of the surface silanol groups has only a small temperature dependence in this range. A Langmuir-type adsorption model was used to express the degree of rate depression for a given in situ pH and Al(OH) 4 − concentration. Incorporation of the rate data in the absence of aluminate into models that assume a first-order dependence of the rate on the fraction of deprotonated silanol sites was unsuccessful. However, the data are consistent with the hypothesis proposed in the literature that two dissolution mechanisms may be operative in alkaline solutions: nucleophilic attack of water on siloxane bonds catalyzed by the presence of a deprotonated silanol group and OH − attack catalyzed by the presence of a neutral silanol group. The data support the dominance of the second mechanism at higher pH and temperature.

Variable Temperature Single‐Molecule Dynamics of MEH‐PPV

Herein, we continue our investigation of the single-molecule spectroscopy of the conjugated polymer poly[2-methoxy,5-(2'-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) at cryogenic temperatures. First, the low temperature microsecond dynamics of single MEH-PPV conjugated polymer molecules are compared to the dynamics at room temperature revealing no detectible temperature dependence. The lack of temperature dependence is consistent with the previous assignment of the dynamics to a mechanism that involves intersystem crossing and triplet-triplet annihilation. Second, the fluorescence spectra of single MEH-PPV molecules at low temperature are studied as a function of excitation wavelength (i.e. 488, 543, and 568 nm). These results exhibit nearly identical fluorescence spectra for different excitation wavelengths. This strongly suggests that electronic energy transfer occurs efficiently to a small number of low-energy sites in the multichromophoric MEH-PPV chains.

Understanding Intramolecular Electron Transfer in Ferredoxin: A Molecular Dynamics Study

An important question about electron-transfer proteins is how the environment of the redox site created by the protein’s matrix affects their electron-transfer properties. Here, we investigate intramolecular electron transfer in the [4Fe-4S] ferredoxins, which are a class of iron-sulfur electron-transfer proteins found in numerous electron transport chains, including the photosynthetic pathway. These proteins are characterized by having two [4Fe-4S] clusters, often but not always with the same reduction potential, and by the pseudo2-fold symmetry of the protein backbone. The nuclear polarization is calculated from molecular dynamics simulations of Clostridrium acidiurici ferredoxin, with a total of 6 ns of simulation, and is then used to calculate free energy reaction curves. In addition, we present here a new method, referred to as the Gaussian parabola method, for obtaining the reaction energy ¢G° and the reorganization energy I from the mean and fluctuations of the polarization, which is based on the linear response of a system with Gaussian fluctuations. For ferredoxin, the calculated outer sphere I is small (<200 meV) and is consistent with the lack of temperature dependence in experimental measurements of rates for this protein; however, the rate calculated from the calculated I is consistent with experimental values if the inner sphere I is large. The calculations also indicate that the contribution of the protein to I is smaller than that of the solvent, which implies that the protein enhances the rate of electron transfer by providing an environment that has a low reorganization energy.

Relationships between nucleic acid levels and egg production rates in Acartia bifilosa: implications for growth assessment of copepods in situ

To evaluate the applicability of RNA-based indices in copepod growth assessment, concentrations of nucleic acids in Acartia bifilosa were calibrated against growth rates estimated via egg production experiments, and the relationships between levels of RNA, DNA, and the RNA:DNA ratio and growth rates were examined. Furthermore, to investigate effects of temperature and food availability on the relationships between weight-specific fecundity and nucleic acid levels, incu- bations were carried out at 9 and 16°C, each at 3 food concentrations. There were positive relation- ships between nucleic acid concentrations and their ratios and weight-specific egg production rates. Overall, RNA concentration was the best predictor of specific growth rate. No correlations between either of the measured variables and female body size were observed. When egg production was ele- vated by manipulating the feeding regime, RNA concentration and the RNA:DNA ratio increased in concert. Neither growth nor RNA indices were significantly affected by temperature, while a signifi- cant increase in DNA concentrations was observed at high food levels and low temperatures. The lack of temperature dependence in RNA-growth relationships allows their direct application for in situ growth estimates in summer populations of A. bifilosa in the northern Baltic Proper.

Studies of the Formation of Poly(ester rotaxane)s from Diacid Chlorides, Diols, and Crown Ethers and Their Properties

The formation of poly(alkylene sebacate−crown ether pseudorotaxane)s by condensation of linear alkylene diols and sebacoyl chloride in the presence of crown ethers in the neat state has been studied. It was found that the average number of crown ether molecules per repeat unit in the polypseudorotaxane was a function of (a) the ring size and (b) the stoichiometric ratio of macrocycle to diol but independent of (i) the equilibration time of the diol and crown ether prior to addition of the diacid chloride, (ii) the length of the diol, and (iii) the temperature of equilibration and polycondensation. All of these observations are consistent with the involvement of hydrogen bonding between the diol and the crown ether as a driving force for threading, except the lack of temperature dependence. Dethreading of the isolated polypseudorotaxanes was shown to be extremely slow. Therefore, it was reasoned that the lack of temperature dependence was due to dethreading during the polymerization, inasmuch as once the ester bond has formed there is no strongly attractive force between the linear and cyclic species and the low molecular weights of the growing oligomeric esters would permit relatively facile dethreading. Based on this idea, a bulky tetraphenylmethane-based bisphenol was employed to make a copolymer (1:4) with 1,10-decanediol; indeed, the purified polyrotaxane contained more than twice as much crown ether as the polypseudorotaxane from the linear diol, confirming that dethreading does occur during the polymerization process. The polyrotaxanes all were capable of extracting metal ions from aqueous solutions. In the cases with high loadings of crown ether two distinct crystalline phases were detected by DSC: one due to the polyester backbone and one due to the crown ether; glass transitions were also observed for the crown ether component of the polyrotaxanes. Polyrotaxanes possess higher intrinsic viscosities than the backbone polymers of the same molecular weight due to increased hydrodynamic volume brought about by the macrocyclic components. However, differential solvation of the backbone and cyclic components of the polyrotaxanes was demonstrated; the intrinsic viscosity of the polyrotaxane decreased in a good solvent for the crown ether. The temperature dependence of the melt viscosity of a polyrotaxane was essentially the same as that of the polyester model backbone, but the absolute melt viscosity was much lower due to reduced chain entanglement.

Virial expansion of the positron and positronium decay rate in a dilute gas: The linear contribution

A systematic theory of the lifetimes of positrons or positronium atoms in a low-density gas is lacking. This paper describes our recent efforts to fill this void. In analogy with the virial expansion for the pressure of a gas, we develop a quantum virial expansion for the properties of a low-mass particle thermalized in a dilute gas. The discrete Feynman path integral is employed to numerically evaluate the quantum traces that comprise the coefficients of each power of the density. By considering two applications of the linear contribution, positron and ortho-positronium decay in xenon, we show how the temperature dependence of the decay rate depends on the interaction between the light particle and an atom. We also explain the observed lack of temperature dependence in experimental measurements of the ortho-positronium pick-off decay rate observed in most gases.

Temperature dependence of the collisional quenching of singlet molecular oxygen (O 2(a 1Δ g) and O 2(b 1Σ g+)) by SO 2

Between 600 K and 1150 K the rate constant for the collisional quenching of O 2(a 1Δ g) by SO 2 was found to be ▪ Extrapolation to 295 K gives a value of 2.5 ± 0.8) × 10 3 dm 3 mol −1 s −1, which is consistent with limits obtained from measurements made at room temperature. At 295 K the rate constant for the quenching of O 2(b 1Σ g +) by SO 2 is (2.5 ± 0.5) × 10 5 dm 3 mol −1 s −1. It does not increase appreciably with temperature up to 1150 K, so that SO 2 provides an exception to our classification of the quenchers of O 2(b 1Σ g +) according to their efficiency at room temperature and their temperature dependence. The lack of temperature dependence has enabled us to verify our previous results with O 2 itself.

Temperature dependence in the MCD spectrum of horseradish peroxidase compound I

Ater considerable experimental study, the analysis of ENDOR [1, 2], and magnetic circular dichroism (MCD) spectra of horseradish peroxidase (HRP) compound I [3], as well as the MCD spectra of a series of porphyrin π-cation radical species [4] has led to the confirmation that the electronic configuration of the heme in the compound I species was that of an Fe(IV) porphyrin π-cation complex. While the MCD data of the enzyme were measured at 273 K, and these spectra can be obtained at low temperatures, the ENDOR [1] and EPR [5] signals can only be detected below 30 K. The MCD experiment is very sensitive to ground state degeneracy and in this paper spectra of HRP compound I are discussed that were obtained between liquid helium temperatures and 100 K. Figure 1 shows how the reduction in temperature has a far more pronounced effect on the MCD spectrum of HRP compound I than on the comparable absorption spectrum. While there are only slight changes in the MCD spectrum between 273 K and ▪ 30 K, there are very dramatic changes between 30 K and 4 K. Below 30 K, there is a loss in intensity at 660 nm with a corresponding increase in the 640 nm band and an increase in the dominance of the 300 nm to 500 nm region by the 420 nm and 460 nm bands. The temperature dependent band at 420 nm appears to be derived from a small impurity of the photochemical product of HRP compound I [6] which is formed during preparation of the sample and as a consequence of the visible and UV light used to measure the MCD spectra. The most striking feature of the spectrum below 30 K is the is the apparent relationship between the 640 nm and 660 nm bands, and the simple intensity increase with inverse temperature that is observed in the 460 nm and 640 nm bands. The latter effect is characteristic of a C term and thus indicates the presence of an orbitally degenerate ground state. Coupling between the S = 1 iron and the S = 1 2 porphyrin to form the degenerate ground state as a set of three Kramers doublets has been used to explain the observations of the temperature dependence of the EPR spectrum [5]; this hypothesis can also be used to describe the appearance of the MCD C term [7]. The lack of temperature dependence above 30 K suggests that the iron and the porphyrin radical are not now strongly coupled together. These data also suggest that a structural change has occured at the low temperatures which results in the temperature dependence in the MCD spectrum as the result of a change in the coupling between the S = 1 iron and the S = 1 2 π-cation porphyrin radical, and the formation of a degenerate ground state.

The lack of temperature-dependence of the specific rotation of cyclomaltohexaose in water-dimethyl sulfoxide mixtures

The lack of temperature-dependence of the specific rotation of cyclomaltohexaose in water-dimethyl sulfoxide mixtures

The phonon spectra of the superionic conductor KBiF 4 (a CaF 2 Analogue)

Theoretical calculations of the phonon infrared and Raman response in simple superionic conductors such as AgI, CuI, and CaF 2 types are based on two fundamental assumptions. First, most of the response can be understood in terms of a breakdown of the selection rules due to disorder (lack of translational symmetry) and second, harmonic lattice dynamics can be used with a good degree of accuracy. This is tested here experimentally in the superionic conductor K 1−xBi 1+xF 4+2x which has the CaF 2 structure (x=0.0 is analogous to 2CaF 2). By varying x we increase the disorder (via F-ion interstitials and vacancies) and measure broad temperature independent reduced Raman and infrared responses. The broad response is dependent on x in a manner consistent with the first assumption and the lack of temperature dependence is consistent with the second assumption. In order to understand the transverse optic vibrational frequencies (ω TO) we have found that plots of ω TO 2vs. μ -1 (reduced mass) are very helpful. The linearity of such plots, for example, for tetrahedrally bonded AgI, CuI, CuBr, CuCl (formal charge Z=1) and the difference of such results for similar materials but with formal charges of 2, 3, and 4 is surprising and not as yet understood. Other conclusions are discussed at the end of the paper.

Proton tunnelling in chromous acid

The infrared absorption spectra of CrOOH and CrOOD are analysed using a model potential consisting of two back-to-back Morse functions. The v s(OH) band of CrOOH at 1950 cm-1 is assigned as a |1> → |2> transition and the 226 cm-1 band in the far infrared as a |0> → |1> tunnelling mode. The v s(OD) doublet of CrOOD, with peaks at 1923 cm-1 and 1613 cm-1, arises from |0> → |3> and |1> → |2> transitions, as suggested originally by Snyder and Ibers. Approximate v s(OH) and v s(OD) band shapes are calculated. The lack of temperature dependence of the 1650 cm-1 v s(OH) band of CrOOH suggests that a ferrodistortive phase transition occurs slightly below room temperature.

Participation of rotational motion in vibrational relaxation of molecules in condensed media

The vibrational relaxation rate through rotation of diatomic molecules in condensed media is calculated for both the low-barrier and the high-barrier cases using the repulsive potential model. The lack of temperature dependence below a threshold temperature is noted and the inverse isotope effect is found. The vibrational relaxation rate in the low-barrier case when the ground state is approximated by vibration and higher states by rotation is calculated in order to examine the validity of the use of the free-rotation approximation in the ground state. The ratio of the vibrational relaxation rate through rotation to the total vibrational relaxation rate is obtained in order to see the relative contribution of the molecular rotation and lattice vibration to the vibrational relaxation.

Infrared magnetic circular dichroism of myoglobin derivatives

By use of a newly constructed CD instrument, infared magnetic circular dichroism (MCD) spectra were observed for various myoglobin derivatives. The ferric high spin myoglobin derivatives such as fluoride, water and hydroxide complexes, commonly exhibited the MCD spectra consisting of positive A terms. Therefore, the results reinforced the assignment that the infrared band is the charge transfer transition to the degenerate excited state (e g (dπ)). Since the fraction of A term estimated was ≈80% for myoglobin fluoride and ≈35% for myoglobin water, the effective symmetry for myoglobin fluoride is determined to be as close as D 4h, while that for myoglobin water seems to have lower symmetry components. The ferric low spin derivatives such as myoglobin cyanide, myoglobin imidazole and myoglobin azide showed positive MCD spectra which are very similar to the electronic absorption spectra. These MCD spectra were assigned to the charge transfer transitions from porphyrin π to iron d orbitals on the ground that they were observed only for the ferric low spin groups and insensitive to the axial ligands. The lack of temperature dependence in the MCD magnitude indicated that the MCD spectra are attributable to the Faraday B terms. Deoxymyoglobin, the ferrous high spin derivative, had fairly strong positive MCD around 760 nm with an anisotropy factor (Δε/ε) of 1.4·10 −4. It shows some small MCD bands from 800 to 1800 nm. Among the ferrous low spin derivatives, carbonmonoxymyoglobin did not give any observable MCD in the infrared region while oxymyoglobin seemed to have significant MCD in the range from 700 to 1000 nm.