Thermophysical Properties of Lignocellulose: A Cell-Scale Study Down to 41K

Thermal energy transport is of great importance in lignocellulose pyrolysis for biofuels. The thermophysical properties of lignocellulose significantly affect the overall properties of bio-composites and the related thermal transport. In this work, cell-scale lignocellulose (mono-layer plant cells) is prepared to characterize their thermal properties from room temperature down to ∼40 K. The thermal conductivities of cell-scale lignocellulose along different directions show a little anisotropy due to the cell structure anisotropy. It is found that with temperature going down, the volumetric specific heat of the lignocellulose shows a slower decreasing trend against temperature than microcrystalline cellulose, and its value is always higher than that of microcrystalline cellulose. The thermal conductivity of lignocellulose decreases with temperature from 243 K to 317 K due to increasing phonon-phonon scatterings. From 41 K to 243 K, the thermal conductivity rises with temperature and its change mainly depends on the heat capacity''s change.     

The effect of gamma-irradiation on the temperature dependence of D.C. electrical conductivity of dry bone.

The effect of gamma-irradiation with doses from 10 to 500 kGy on the electrical conductivity (g) of dry bone was studied. Temperature measurement of electrical conductivity were made from 393 to 533 K. The dependence obtained indicates the increase in g with temperature. An increase in irradiation dose resulted in a decreased g value for each dose up to temperature 462 K. Temperature 462 K was interpreted as the temperature of collagen melting point in dry bone. Above 462 K, g values were dose independent. A dose of 500 kGy shifted the melting point to lower temperature. In addition, the activation energy for the charge conduction process was calculated. Obtained values for electrical conductivity and activation energy were typical for dielectrics and indicated degradation of the organic component of bone.     

零上低温对热带绿化树木叶片电阻、水浸液电导率和K~+离子含量的影响

本文报道了在零上低温下6种热带绿化树木叶片电阻、叶片水浸液电导率和K~+离子含量的变化。在非致害零上低温处理下,叶片电阻值增加;在致害零上低温影响下受害时,叶片电阻值减小,叶片水浸液电导率和K~+离子含量平行地增加,这种变化随着伤害的加剧而扩大。     

Electrical conduction through nerve and DNA

The aim of the present study was to analyse electric resistivity at different ambient temperatures between 300 to 20K in the frog sciatic nerve and salmon sperm DNA. When the electrical contacts were leaned just into the sciatic nerve, an increase of the sciatic nerve resistivity was observed for 240 K < T < 300 K and a rise of electrical conductivity was apparent below 240 K. This dependence is generally associated with a semiconductor behaviour. Once the sciatic nerve temperature was driven below 250K, the resistivity abruptly decreased and then at temperatures lower than 234 K, it remained constant and close to one tenth of its ambient temperature value. By contrast, when the electrical contacts were leaned into Salmon sperm DNA, the resistivity remained constant between 300K to 20K, showing a high electrical stability at low temperature. Thus, we report the existence of a new form of electric conductivity in the sciatic nerve at low ambient temperature, which in turn has many electric similarities with inorganic or organic superconductors, whereas temperature failed to alter DNA electrical properties until 20K.     

Large Thermal Conductivity Differences between the Crystalline and Vitrified States of DMSO with Applications to Cryopreservation

Thermal conductivity of dimethyl-sulfoxide (DMSO) solution is measured in this study using a transient hot wire technique, where DMSO is a key ingredient in many cryoprotective agent (CPA) cocktails. Characterization of thermal properties of cryoprotective agents is essential to the analysis of cryopreservation processes, either when evaluating experimental data or for the design of new protocols. Also presented are reference measurements of thermal conductivity for pure water ice and glycerol. The thermal conductivity measurement setup is integrated into the experimentation stage of a scanning cryomacroscope apparatus, which facilitates the correlation of measured data with visualization of physical events. Thermal conductivity measurements were conducted for a DMSO concentration range of 2M and 10M, in a temperature range of -180°C and 25°C. Vitrified samples showed decreased thermal conductivity with decreasing temperature, while crystalline samples showed increased thermal conductivity with decreasing temperature. These different behaviors result in up to a tenfold difference in thermal conductivity at -180°C. Such dramatic differences can drastically impact heat transfer during cryopreservation and their quantification is therefore critical to cryobiology.     

Melatonin-like Immunoreactivity in the Presence of Different Chemicals as Determined by the Radioimmunoassay

To determine the nature of the molecule(s) that is responsible for the melatonin like immunoreactivity (MLI), we measured the effect of pretreatment of plasma samples with detergents, reducing agent, and proteinase K. Nonidet P-40 Triton X-100, and ethylacetate extraction had no effect, while sodium deoxycholate, sodium dodecyl sulfate, β-mercaptoethanol, ether extraction, proteinase K, and temperature increased the MLI. Since the radioimmunoassay (RIA) was sensitive to proteinase K, ionic detergents, and a reducing compound, we hypothesize that a proteinaceous molecule might be responsible for this MLI. We compared our column procedure for RIA of plasma melatonin (1) with procedures involving extraction with either ethylacetate or ether. In our hands preextraction of samples with organic solvents caused a loss of immunoreactivity. We also found that passing samples through the column is more efficient in eliminating interference in the melatonin assay than extracting samples either with ethylacetate or ether.     

DNA溶液的导电行为

将链长不同的两种DNA溶解在超纯水中,分别测定它们在不同浓度不同温度下的电导行为。试验证明,同种DNA的电导率随着溶液中DNA的浓度增大而显著增大。而对于两种不同的DNA,短链DNA(<50bp)的电导能力较长链DNA(>1000bp)好。在本文测试的浓度范围内,短链DNA水溶液常温下电导率达到0.99×10-4S/cm。而且,电导率随DNA浓度的变化规律与指数方程(δ/δ0=aCm)符合得很好。当温度升高时长链和短链DNA溶液的电导率都有明显增大,并且随温度的变化趋势基本一致。     

Relaxation dynamics of a protein solution investigated by dielectric spectroscopy

In the present work, we provide a dielectric study on two differently concentrated aqueous lysozyme solutions in the frequency range from 1MHz to 40GHz and for temperatures from 275 to 330K. We analyze the three dispersion regions, commonly found in protein solutions, usually termed β-, γ-, and δ-relaxations. The β-relaxation, occurring in the frequency range around 10MHz and the γ-relaxation around 20GHz (at room temperature) can be attributed to the rotation of the polar protein molecules in their aqueous medium and the reorientational motion of the free water molecules, respectively. The nature of the δ-relaxation, which is often ascribed to the motion of bound water molecules, is not yet fully understood. Here we provide data on the temperature dependence of the relaxation times and relaxation strengths of all three detected processes and on the dc conductivity arising from ionic charge transport. The temperature dependences of the β- and γ-relaxations are closely correlated. We found a significant temperature dependence of the dipole moment of the protein, indicating conformational changes. Moreover we find a breakdown of the Debye-Stokes-Einstein relation in this protein solution, i.e., the dc conductivity is not completely governed by the mobility of the solvent molecules. Instead it seems that the dc conductivity is closely connected to the hydration shell dynamics.     

The hydraulic conductivity of Matrigel

In this study, we measured the specific hydraulic conductivity (K) of Matrigel at 1% and 2% concentrations as a function of perfusion pressure (0 to 100 mmHg) and compared the results to predictions from two models: a fiber matrix model that predicted K of the gel based upon its composition, and a biphasic model that predicted changes in K caused by pressure induced compaction of the gels. The extent of gel compaction as a function of perfusion pressure was also assessed, allowing us to estimate the stiffness of the gels. As expected, 2% Matrigel had a lower K and a higher stiffness than did 1% Matrigel. Measured values of K of both 1% and 2% Matrigel samples showed good agreement with the predictions of the fiber matrix model. Pressure-induced changes in K were better described by the biphasic model than a model in which uniform compression of the gel was assumed. We conclude that K of multi-component gels, such as Matrigel can be well characterized by fiber matrix models, and that pressure-induced changes in K of such gels can be well characterized by biphasic models.     

Effect of temperature on the photoproperties of luminescent terbium sensors for homogeneous bioassays

We developed a luminescent terbium sensor (LTS) based on energy resonance transfer for homogeneous bioassays. The effect of temperature on photoluminescence and time‐resolved fluorescence of the LTS was investigated. When the temperature was increased from 277 K to 369 K, the photoluminescence quantum yield decreased by up to 25 %, time‐resolved fluorescence decreased by up to 54 %, and the lifetime shortened dramatically. Studies showed that both photoluminescence and time‐resolved fluorescence quantum yields were largely recovered after samples were heated from 298 to 310, 333 or 369 K and subsequently cooled to 298 K. These results indicate that the homogeneous bioassay with LTS is sensitive to temperature and should be conducted at a constant temperature to ensure the temperature effect does not influence data and to increase the accuracy of the results. The results of this study are important for LTS applications in homogeneous bioassays. Copyright © 2012 John Wiley & Sons, Ltd.     

Calorimetric study of crystal growth of ice in hydrated methemoglobin and of redistribution of the water clusters formed on melting the ice.

Calorimetric studies of the melting patterns of ice in hydrated methemoglobin powders containing between 0.43 and 0.58 (g water)/(g protein), and of their dependence on annealing at subzero temperatures and on isothermal treatment at ambient temperature are reported. Cooling rates were varied between approximately 1500 and 5 K min-1 and heating rate was 30 K min-1. Recrystallization of ice during annealing is observed at T > 228 K. The melting patterns of annealed samples are characteristically different from those of unannealed samples by the shifting of the melting temperature of the recrystallized ice fraction to higher temperatures toward the value of "bulk" ice. The "large" ice crystals formed during recrystallization melt on heating into "large" clusters of water whose redistribution and apparent equilibration is followed as a function of time and/or temperature by comparison with melting endotherms. We have also studied the effect of cooling rate on the melting pattern of ice with a methemoglobin sample containing 0.50 (g water)/(g protein), and we surmise that for this hydration cooling at rates of > or = approximately 150 K min-1 preserves on the whole the distribution of water molecules present at ambient temperature.     

Micro-environmental factors and the endemism of bromeliad aquatic fauna

Tank bromeliads harbour aquatic microcosms with many endemic species among their leaves. We performed a set of experiments to determine which factors maintain the bromeliad aquatic fauna in isolation from neighbouring ponds. We cultivated three invertebrates species (an ostracod, an annelid and a cladoceran) from a pond surrounded by terrestrial bromeliads in Southeastern Brazil and introduced them inside cleaned bromeliads, using recipients with the same volume as controls. The pH, conductivity and organism densities were monitored in the bromeliad samples and controls for 41 days. The samples introduced inside the cleaned bromeliads showed a significant decrease in pH and conductivity compared to the controls. The pond organism populations introduced in the bromeliads presented a high extinction rate and a significant population decrease when compared to the ones introduced in the controls. We attributed the population decline experienced by the pond organisms to the oligotrophic conditions generated inside the tanks by the bromeliads due to the nutrient absorption. We suggest that the changes in water chemistry induced by the bromeliads could play an important role in isolating their microcosm communities from other freshwater systems. Other mechanisms that could produce the high rates of endemism in bromeliad fauna are discussed. Handling editor: K. Martens     

Electrical conductivity in the solid state of sodium salts of calf thymus DNA

A dc conductivity study of native and denatured samples of sodium salts of calf thymus DNA in the solid state was performed at different temperatures and water content. From the results obtained it appears that the major carrier of conductivity is either electronic or ionic, depending upon the temperature of the sample, the water content, and the fact that the conductivity of native samples is higher than that of the denatured ones. These results have been confirmed by dc conductivity studies of poly U and poly A.     

Temporary Changes in the dc ElectricalConductivity of MX (3-Chloro-4(Dichloromethyl)-5-Hydroxy-2(5H)-Furanone) Treated Collagen

The influence of MX(3-Chloro-4(Dichloromethyl)-5-Hydroxy-2(5H)- Furanone), a stronglymutagenic compound, on the temperature dependence of the dcelectrical conductivity of collagen as a function of time was studied.Collagen was immersed in MX solution, next dried and pressed intotablets. The MX concentration was measured by HPLC analysis.The reduction of MX concentration to 10% of the initial value wasobserved in the presence of collagen in the solution, whereas in thecontrol solution concentration of MX decreased to 70% of the initialvalue. Measurements of electrical conductivity were performed for thetemperature range 295–453K and activation energies for the chargeconduction process were calculated. Within the temperature range295–340K, the presence of MX decreased electrical conductivity ofcollagen. Calculated activation energies were typical for dry proteins.Within the temperature range 295–320K activation energy decreasedwith time, probably due to the stronger interactions in thecollagen-water-MX system. For temperatures between 320–410 and430–450K the activation energy was not time dependent and theapplication of MX did not change the structure of the collagenmacromolecule. The temporary changes occurring at the lowertemperatures being due solely to changes in the collagen-waterinteractions.     

Measurement of the Thermal Conductivity of Unfrozen and Frozen Food Materials by a Steady State Method with Coaxial Dual-cylinder Apparatus

Coaxial dual-cylinder apparatus was used to measure the effective thermal conductivity of aqueous solutions of glucose, sucrose, gelatin and egg albumin over a temperature range from –20° to 20°C by the steady state method. The accuracy of the apparatus was confirmed by testing with water and ice. The effective thermal conductivity decreased with an increase in the total solid content in both the frozen and unfrozen states. In the unfrozen state, the effective thermal conductivity was slightly dependent on temperature. In the frozen state, however, the effective thermal conductivity was strongly dependent on temperature; lower temperatures gave higher effective thermal conductivity, reflecting the increase in the ice fration. For the unfrozen samples, the intrinsic thermal conductivity of each solid component was calculated by heat transfer models. All the models tested, series, parallel and Maxwell–Eucken, were equally applicable to describe the heat conduction in the unfrozen state. In the frozen state, however, the strong temperature dependency of the effective thermal conductivity suggests that the effect of the temperature dependency of the ice fraction should be incorporated into theoretical models.     

Improving xylem hydraulic conductivity measurements by correcting the error caused by passive water uptake

Xylem hydraulic conductivity (K) is typically defined as K = F/(P/L), where F is the flow rate through a xylem segment associated with an applied pressure gradient (P/L) along the segment. This definition assumes a linear flow-pressure relationship with a flow intercept (F(0) ) of zero. While linearity is typically the case, there is often a non-zero F(0) that persists in the absence of leaks or evaporation and is caused by passive uptake of water by the sample. In this study, we determined the consequences of failing to account for non-zero F(0) for both K measurements and the use of K to estimate the vulnerability to xylem cavitation. We generated vulnerability curves for olive root samples (Olea europaea) by the centrifuge technique, measuring a maximally accurate reference K(ref) as the slope of a four-point F vs P/L relationship. The K(ref) was compared with three more rapid ways of estimating K. When F(0) was assumed to be zero, K was significantly under-estimated (average of -81.4 ± 4.7%), especially when K(ref) was low. Vulnerability curves derived from these under-estimated K values overestimated the vulnerability to cavitation. When non-zero F(0) was taken into account, whether it was measured or estimated, more accurate K values (relative to K(ref) ) were obtained, and vulnerability curves indicated greater resistance to cavitation. We recommend accounting for non-zero F(0) for obtaining accurate estimates of K and cavitation resistance in hydraulic studies.     

Enhancement of Thermoelectric Figure of Merit by the Insertion of MgTe Nanostructures in p‐type PbTe Doped with Na2Te

The thermoelectric properties of crystalline melt‐grown ingots of p‐type PbTe–xMgTe (x = 1–3 mol%) doped with Na₂Te (1–2 mol%) were investigated over the temperature range of 300 K to 810 K. While the powder X‐ray diffraction patterns show that all samples crystallize in the NaCl‐type structure with no MgTe or other phases present, transmission electron microscopy reveals ubiquitous MgTe nanoprecipitates in the PbTe. The very small amounts of MgTe in PbTe have only a small effect on the electrical transport properties of the system, while they have a large effect on thermal transport significantly reducing the lattice thermal conductivity. A ZT of 1.6 at 780 K is achieved for the PbTe containing 2% MgTe doped with 2% Na₂Te.     

Active and resting states of the O2-evolving complex of photosystem II

During dark adaptation, a change in the O2-evolving complex (OEC) of spinach photosystem II (PSII) occurs that affects both the structure of the Mn site and the chemical properties of the OEC, as determined from low-temperature electron paramagnetic resonance (EPR) spectroscopy and O2 measurements. The S2-state multiline EPR signal, arising from a Mn-containing species in the OEC, exhibits different properties in long-term (4 h at 0 degrees C) and short-term (6 min at 0 degree C) dark-adapted PSII membranes or thylakoids. The optimal temperature for producing this EPR signal in long-term dark-adapted samples is 200 K compared to 170 K for short-term dark-adapted samples. However, in short-term dark-adapted samples, illumination at 170 K produces an EPR signal with a different hyperfine structure and a wider field range than does illumination at 160 K or below. In contrast, the line shape of the S2-state EPR signal produced in long-term dark-adapted samples is independent of the illumination temperature. The EPR-detected change in the Mn site of the OEC that occurs during dark adaptation is correlated with a change in O2 consumption activity of PSII or thylakoid membranes. PSII membranes and thylakoid membranes slowly consume O2 following illumination, but only when a functional OEC and excess reductant are present. We assign this slow consumption of O2 to a catalytic reduction of O2 by the OEC in the dark. The rate of O2 consumption decreases during dark adaptation; long-term dark-adapted PSII or thylakoid membranes do not consume O2 despite the presence of excess reductant.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ionic content in plant extracts determined by ion chromatography with conductivity detection

A simple method is described for the determination of the ionic content of vegetable samples by ion chromatography with suppressed conductivity detection. Extracts of leaves of cucumber (Cucumis sativus), leaves and cotyledons of watermelon (Citrullus lanantus), cotyledons of zucchini (Cucurbitapepo), and leaves and roots of olive (Olea europaea) obtained at room temperature yielded chromatographic profiles with substantial differences in the relative contents of Cl-, NO3-, HPO4(2-) and SO4(2-) as well as of Na+, NH4+, K+, Mg2+ and Ca2+. Although NO3-, Cl- and K+ were common to each extracted sample and accounted for most of the ions present, two additional anion peaks (i.e. malate and oxalate) were detected. Among the vegetable tissues investigated, olive roots contained a considerable amount of oxalate (37 mg/g dry weight), while Na+, which is present in very low amount in extracted samples of leaves and cotyledons, represented ca. 30% of the cationic content of olive roots. In all the examined tissue extracts, K+ was the main cation (16-55 mg/g dry weight) and NO3-, Cl- and HPO4(2-) were the main inorganic anions.     

Variation in hydraulic conductivity of mangroves: influence of species, salinity, and nitrogen and phosphorus availability

We investigated how species identity and variation in salinity and nutrient availability influence the hydraulic conductivity of mangroves. Using a fertilization study of two species in Florida, we found that stem hydraulic conductivity expressed on a leaf area basis ( K _leaf) was significantly different among species of differing salinity tolerance, but was not significantly altered by enrichment with limiting nutrients. Reviewing data from two additional sites (Panamá and Belize), we found an overall pattern of declining leaf‐specific hydraulic conductivity ( K _leaf) with increasing salinity. Over three sites, a general pattern emerges, indicating that native stem hydraulic conductivity ( K _h) and K _leaf are less sensitive to nitrogen (N) fertilization when N limits growth, but more sensitive to phosphorus (P) fertilization when P limits growth. Processes leading to growth enhancement with N fertilization are probably associated with changes in allocation to leaf area and photosynthetic processes, whereas water uptake and transport processes could be more limiting when P limits growth. These findings suggest that whereas salinity and species identity place broad bounds on hydraulic conductivity, the effects of nutrient availability modulate hydraulic conductivity and growth in complex ways.