共查询到20条相似文献,搜索用时 31 毫秒
1.
Thermally Stimulated Depolarization Currents (TSDC) measurements on α-d-glucose have been carried out in the temperature region from −165 °C (108 K) to 120 °C (393 K). The slow molecular mobility was characterized in the crystalline and in the glassy states, as well as in the glass transition region. The influence of aging on the measured TSDC peaks of the secondary relaxation has been discussed and it was concluded that there are motional modes that are aging independent while others are affected by aging. Important discrepancies were reported in the value of the steepness index or fragility (Tg—normalized temperature dependence of the relaxation time) obtained by different, and well-established, experimental techniques. A careful discussion of the possible origins of these discrepancies is presented. 相似文献
2.
S. Khodadadi A. MalkovskiyA. Kisliuk A.P. Sokolov 《Biochimica et Biophysica Acta - Proteins and Proteomics》2010,1804(1):15-19
We performed Raman and Brillouin scattering measurements to estimate glass transition temperature, Tg, of hydrated protein. The measurements reveal very broad glass transition in hydrated lysozyme with approximate Tg ∼ 180 ± 15 K. This result agrees with a broad range of Tg ∼ 160–200 K reported in literature for hydrated globular proteins and stresses the difference between behavior of hydrated biomolecules and simple glass-forming systems. Moreover, the main structural relaxation of the hydrated protein system that freezes at Tg ∼ 180 K remains unknown. We emphasize the difference between the “dynamic transition”, known as a sharp rise in mean-squared atomic displacement <r2> at temperatures around TD ∼ 200–230 K, and the glass transition. They have different physical origin and should not be confused. 相似文献
3.
Manuel Quesada Olivier Roubeau Simon J. Teat Jaap G. Haasnoot 《Inorganica chimica acta》2007,360(13):3787-3796
The reaction of 1,3-bis(tetrazol-1-yl)-2-propanol (btzpol) with Fe(BF4)2 · 6H2O in acetonitrile yields the remarkable 2D coordination polymer [FeII(btzpol)1.8(btzpol-OBF3)1.2](BF4)0.8 · (H2O)0.8(CH3CN) (1). This compound has been structurally characterized using an X-ray single-crystal synchrotron radiation source. The iron(II) centers are bridged by means of double btzpol bridges along the c direction, and by single btzpol bridges along the b direction. The reaction of part of the ligand with the counterion has forced the compound to crystallize in this extended two dimensional structure. The compound shows spin-transition properties, both induced by temperature and light, with T1/2 = 112 K and T(LIESST) = 46 K, respectively. The relaxation of the metastable high-spin state created by irradiation is exponential, following an Arrhenius type behavior at high temperature, and dominated by a temperature independent tunneling process at lower temperatures. 相似文献
4.
Hiromasa Hara Miho Tagiri In-Sul Hwang Masato Takahashi Masumi Hirabayashi Shinichi Hochi 《Cryobiology》2014
Under optimal freeze-drying conditions, solutions exhibit a cake-like porous structure. However, if the solution temperature is higher than the glass transition temperature of the maximally freeze-concentrated phase (Tg′) during drying phase, the glassy matrix undergoes viscous flow, resulting in cake collapse. The purpose of the present study was to investigate the effect of cake collapse on the integrity of freeze-dried bull spermatozoa. In a preliminary experiment, factors affecting the Tg′ of conventional EGTA buffer (consisting of Tris–HCl, EGTA and NaCl) were investigated in order to establish the main experimental protocol because EGTA buffer Tg′ was too low (−45.0 °C) to suppress collapse. Modification of the EGTA buffer composition by complete removal of NaCl and addition of trehalose (mEGTA buffer) resulted in an increase of Tg′ up to −27.7 °C. In the main experiment, blastocyst yields after ooplasmic injection of freeze-dried sperm preserved in collapsed cakes (drying temperature: 0 or −15 °C) were significantly lower than those of sperm preserved in non-collapsed cake (drying temperature: −30 °C). In conclusion, freeze-dried cake collapse may be undesirable for maintaining sperm functions to support embryonic development, and can be inhibited by controlling both Tg′ of freeze-drying buffer and temperature during the drying phase. 相似文献
5.
A model mineralizing system was subjected to magnetic resonance microscopy to investigate how water proton transverse (T2) relaxation times and magnetization transfer ratios can be applied to monitor collagen mineralization. In our model system, a collagen sponge was mineralized with polymer-stabilized amorphous calcium carbonate. The lower hydration and water proton T2 values of collagen sponges during the initial mineralization phase were attributed to the replacement of the water within the collagen fibrils by amorphous calcium carbonate. The significant reduction in T2 values by day 6 (p < 0.001) was attributed to the appearance of mineral crystallites, which were also detected by x-ray diffraction and scanning electron microscopy. In the second phase, between days 6 and 13, magnetic resonance microscopy properties appear to plateau as amorphous calcium carbonate droplets began to coalesce within the intrafibrillar space of collagen. In the third phase, after day 15, the amorphous mineral phase crystallized, resulting in a reduction in the absolute intensity of the collagen diffraction pattern. We speculate that magnetization transfer ratio values for collagen sponges, with similar collagen contents, increased from 0.25 ± 0.02 for control strips to a maximum value of 0.31 ± 0.04 at day 15 (p = 0.03) because mineral crystals greatly reduce the mobility of the collagen fibrils. 相似文献
6.
The annealing behaviour of a spray-dried maltodextrin was investigated by differential scanning calorimetry. Special attention was paid to the effect of temperature and humidity on the annealing process. Comparison was also made with the glassy state of the same compound prepared by various cooling processes. The presence of a very pronounced sub-Tg peak upon ageing reveals the specificities of the glass and the complexity of the relaxation spectrum of the spray-dried material. This peak seems actually to correspond to a partial ergodicity recovery that may be attributed to onset of molecular mobility occurring below Tg. The position of the sub-Tg peak with regard to the conventional Tg was systematically studied. It clearly showed the difference between the effect of temperature and water plasticization on the relaxations occurring in the glassy state of materials prepared by spray-drying. 相似文献
7.
Kamil Kaminski Ewa Kaminska Patryk Wlodarczyk Jerzy Ziolo Wies?aw Szeja Jerzy Pilch 《Carbohydrate research》2009,344(18):2547-3633
Dielectric relaxation measurements were performed on two enantiomers, d- and l-arabinose and their equimolar mixture, and compared to dielectric data obtained for d-ribose. d-Arabinose differs from d-ribose by having the opposite configuration at C2. This study reveals that both d- and l- of arabinose exhibit α-relaxation peaks with the same shape for the same α-relaxation time τα, and the same steepness index for the Tg-scale T-dependence of τα. However, the two isomers have slightly different glass transition temperatures Tg’s, and their secondary γ-relaxation times also differ slightly from the previously observed γ-relaxation in d-ribose at the same temperature. However, when samples of both investigated monosaccharides are annealed at higher temperatures, their glass transition temperatures become nearly identical. This is an effect of the mutarotation process, which leads to the formation of pairs of the enantiomers and accordingly they should have the same physical properties. The width of the α-relaxation of d- and l-arabinose is broader than that of d-ribose, as reflected by the smaller stretch exponent in the Kohlrausch-Williams-Watts function used to fit the data of the former (βKWW = 0.46 ± 0.01) than the latter (βKWW = 0.55 ± 0.01). The width of the α-relaxation of racemic mixture of the d- and l-arabinose is slightly broader than that of the pure isomers. While the dielectric loss data of d-ribose in the glassy state at ambient and elevated pressures show an inflexion indicating the presence of the JG β-relaxation, the data of d- and l-arabinose show no such feature for identification of the supposedly universal JG β-relaxation. Nevertheless, on comparing the loss spectra of d-arabinose with that of d-ribose, the presence of the JG β-relaxation in d-arabinose has been rationalized. 相似文献
8.
Robert C. Jennings Enrico Engelmann Flavio Garlaschi Anna Paola Casazza Giuseppe Zucchelli 《BBA》2005,1709(3):251-255
The widely held view that the maximum efficiency of a photosynthetic pigment system is given by the Carnot cycle expression (1 − T/Tr) for energy transfer from a hot bath (radiation at temperature Tr) to a cold bath (pigment system at temperature T) is critically examined and demonstrated to be inaccurate when the entropy changes associated with the microscopic process of photon absorption and photochemistry at the level of single photosystems are considered. This is because entropy losses due to excited state generation and relaxation are extremely small (ΔS ? T/Tr) and are essentially associated with the absorption-fluorescence Stokes shift. Total entropy changes associated with primary photochemistry for single photosystems are shown to depend critically on the thermodynamic efficiency of the process. This principle is applied to the case of primary photochemistry of the isolated core of higher plant photosystem I and photosystem II, which are demonstrated to have maximal thermodynamic efficiencies of ξ > 0.98 and ξ > 0.92 respectively, and which, in principle, function with negative entropy production. It is demonstrated that for the case of ξ > (1 − T/Tr) entropy production is always negative and only becomes positive when ξ < (1 − T/Tr). 相似文献
9.
The decay kinetics of the aminoethanol-generated CoII-substrate radical pair catalytic intermediate in ethanolamine ammonia-lyase from Salmonella typhimurium have been measured on timescales of <105 s in frozen aqueous solution from 190 to 217 K. X-band continuous-wave electron paramagnetic resonance (EPR) spectroscopy of the disordered samples has been used to continuously monitor the full radical pair EPR spectrum during progress of the decay after temperature step reaction initiation. The decay to a diamagnetic state is complete and no paramagnetic intermediate states are detected. The decay exhibits three kinetic regimes in the measured temperature range, as follows. i), Low temperature range, 190 ≤ T ≤ 207 K: the decay is biexponential with constant fast (0.57 ± 0.04) and slow (0.43 ± 0.04) phase amplitudes. ii), Transition temperature range, 207 < T < 214 K: the amplitude of the slow phase decreases to zero with a compensatory rise in the fast phase amplitude, with increasing temperature. iii), High temperature range, T ≥ 214 K: the decay is monoexponential. The observed first-order rate constants for the monoexponential (kobs,m) and the fast phase of the biexponential decay (kobs,f) adhere to the same linear relation on an lnk versus T−1 (Arrhenius) plot. Thus, kobs,m and kobs,f correspond to the same apparent Arrhenius prefactor and activation energy (logAapp,f (s−1) = 13.0, Ea,app,f = 15.0 kcal/mol), and therefore, a common decay mechanism. We propose that kobs,m and kobs,f represent the native, forward reaction of the substrate through the radical rearrangement step. The slow phase rate constant (kobs,s) for 190 ≤ T ≤ 207 K obeys a different linear Arrhenius relation (logAapp,s (s−1) = 13.9, Ea,app,s = 16.6 kcal/mol). In the transition temperature range, kobs,s displays a super-Arrhenius increase with increasing temperature. The change in Ea,app,s with temperature and the narrow range over which it occurs suggest an origin in a liquid/glass or dynamical transition. A discontinuity in the activation barrier for the chemical reaction is not expected in the transition temperature range. Therefore, the transition arises from a change in the properties of the protein. We propose that a protein dynamical contribution to the reaction, which is present above the transition temperature, is lost below the transition temperature, owing to an increase in the activation energy barrier for protein motions that are coupled to the reaction. For both the fast and slow phases of the low temperature decay, the dynamical transition in protein motions that are obligatorily coupled to the reaction of the CoII-substrate radical pair lies below 190 K. 相似文献
10.
The copper(II) complex with tolfenamic acid [Cu(tolf)2(H2O)]2 was studied by X-band and K-band EPR spectroscopies in the temperature range from 90 to 300 K. The Cu2+ ions in dinuclear complex show a strong antiferromagnetic exchange interaction with |J| = 292 cm−1. The EPR spectra, which were observed for [Cu(tolf)2(H2O)]2, are typical powder spectra of the copper pairs. The spectra exhibit the hyperfine structure in low temperature range. The values of the spin-Hamiltonian parameters were determined on the basis of the best fit for the simulated spectra at both K-band (0.75 cm−1) at T = 298 K and X-band (0.3 cm−1) at T = 93 K as compared with the experimentally observed spectra. These values show that the local environment around the copper species is distorted tetragonal pyramid. This EPR evidence is consistent with the crystallographic data. 相似文献
11.
The oxygen evolving complex of Photosystem II undergoes four light-induced oxidation transitions, S0-S1,…,S3-(S4)S0 during its catalytic cycle. The oxidizing equivalents are stored at a (Mn)4Ca cluster, the site of water oxidation. EPR spectroscopy has yielded valuable information on the S states. S2 shows a notable heterogeneity with two spectral forms; a g = 2 (S = 1/2) multiline, and a g = 4.1 (S = 5/2) signal. These oscillate in parallel during the period-four cycle. Cyanobacteria show only the multiline signal, but upon advancement to S3 they exhibit the same characteristic g = 10 (S = 3) absorption with plant preparations, implying that this latter signal results from the multiline configuration. The fate of the g = 4.1 conformation during advancement to S3 is accordingly unknown. We searched for light-induced transient changes in the EPR spectra at temperatures below and above the half-inhibition temperature for the S2 to S3 transition (ca 230 K). We observed that, above about 220 K the g = 4.1 signal converts to a multiline form prior to advancement to S3. We cannot exclude that the conversion results from visible-light excitation of the Mn cluster itself. The fact however, that the conversion coincides with the onset of the S2 to S3 transition, suggests that it is triggered by the charge-separation process, possibly the oxidation of tyr Z and the accompanying proton relocations. It therefore appears that a configuration of (Mn)4Ca with a low-spin ground state advances to S3. 相似文献
12.
α-Amylase from Sorghum bicolor, is reversibly unfolded by chemical denaturants at pH 7.0 in 50 mM Hepes containing 13.6 mM calcium and 15 mM DTT. The isothermal equilibrium unfolding at 27 °C is characterized by two state transition with ΔG (H2O) of 16.5 kJ mol−1 and 22 kJ mol−1, respectively, at pH 4.8 and pH 7.0 for GuHCl and ΔG (H2O) of 25.2 kJ mol−1 at pH 4.8 for urea. The conformational stability indicators such as the change in excess heat capacity (ΔCp), the unfolding enthalpy (Hg) and the temperature at ΔG = 0 (Tg) are 17.9 ± 0.7 kJ mol−1 K−1, 501.2 ± 18.2 kJ mol−1 and 337.3 ± 6.9 K at pH 4.8 and 14.3 ± 0.5 kJ mol−1 K−1, 509.3 ± 21.7 kJ mol−1 and 345.4 ± 4.8 K at pH 7.0, respectively. The reactivity of the conserved cysteine residues, during unfolding, indicates that unfolding starts from the ‘B’ domain of the enzyme. The oxidation of cysteine residues, during unfolding, can be prevented by the addition of DTT. The conserved cysteine residues are essential for enzyme activity but not for the secondary and tertiary fold acquired during refolding of the denatured enzyme. The pH dependent stability described by ΔG (H2O) and the effect of salt on urea induced unfolding confirm the role of electrostatic interactions in enzyme stability. 相似文献
13.
A new complex of composition [Cu(2-NO2bz)2(nia)2(H2O)2] (1) (nia = nicotinamide, 2-NO2bz = 2-nitrobenzoate) has been prepared and its composition and stereochemistry as well as coordination mode have been determined by elemental analysis, electronic, infrared and EPR spectroscopy, magnetization measurements over the temperature range 1.8-300 K, and its structure has been solved, as well. The complex structure consists of the centrosymmetric molecules with Cu(II) atom monodentately coordinated by the pair of 2-nitrobenzoato anions and by the pair of nicotinamide molecules, forming nearly tetragonal basal plane, and by a pair of water molecules that complete tetragonal-bipyramidal coordination polyhedron about the copper atom. The complex 1 exhibits magnetic moment μeff = 1.86 B.M. at 300 K which decreases to μeff = 1.83 B.M. at 1.8 K. The magnetic susceptibility temperature dependence obeys Curie-Weiss law with Curie constant of 0.442 cm3 K mol−1 and with Weiss constant of −1.0 K. EPR spectra at room temperature as well as at 77 K are of axial type with g⊥ = 2.065 and g∥ = 2.280 and exhibit clearly, but partially resolved parallel hyperfine splitting with AII = 160 G, that is consistent with the determined molecular structure of 1. In order to analyze the factors influencing the degree of tetragonal distortion of coordination polyhedron, the dataset of 72 structures similar to that of 1 was extracted from CCD and analyzed. A significant correlation between the average Cu-Oax bond length and tetragonality parameter τ which was found as a consequence of the Jahn-Teller effect. 相似文献
14.
Remote measurements of body temperature (Tb) in animals require implantation of relatively large temperature-sensitive radio-transmitters or data loggers, whereas rectal temperature (Trec) measurements require handling and therefore may bias the results. We investigated whether ∼0.1 g temperature-sensitive subcutaneously implanted transponders can be reliably used to quantify thermal biology and torpor use in small mammals. We examined (i) the precision of transponder readings as a function of temperature and (ii) whether subcutaneous transponders can be used to remotely record subcutaneous temperature (Tsub). Five adult male dunnarts (Sminthopsis macroura, body mass 24 g) were implanted with subcutaneous transponders to determine Tsub as a function of time and ambient temperature (Ta), and in comparison to thermocouple readings of Trec. Transponder temperature was highly correlated with water bath temperature (r2=0.96–0.99) over a range of approximately 10.0–40.0 °C. Transponders provided reliable data (±0.6 °C) over the Tsub of 21.4–36.9 °C and could be read from a distance of up to 5 cm. Below 21.4 °C, accuracy was reduced to ±2.8 °C, but individual transponder accuracy varied. Consequently, small subcutaneous transponders are useful to remotely quantify thermal physiology and torpor patterns without having to disturb the animal and disrupt torpor. Even at Tsub<21.4 °C where the accuracy of the temperature readings was reduced, transponders do provide reliable data on whether and when torpor is used. 相似文献
15.
Based on curvature energy considerations, nonbilayer phase-forming phospholipids in excess water should form stable bicontinuous inverted cubic (QII) phases at temperatures between the lamellar (Lα) and inverted hexagonal (HII) phase regions. However, the phosphatidylethanolamines (PEs), which are a common class of biomembrane phospholipids, typically display direct Lα/HII phase transitions and may form intermediate QII phases only after the temperature is cycled repeatedly across the Lα/HII phase transition temperature, TH, or when the HII phases are cooled from T > TH. This raises the question of whether models of inverted phase stability, which are based on curvature energy alone, accurately predict the relative free energy of these phases. Here we demonstrate the important role of a noncurvature energy contribution, the unbinding energy of the Lα phase bilayers, gu, that serves to stabilize the Lα phase relative to the nonlamellar phases. The planar Lα phase bilayers must separate for a QII phase to form and it turns out that the work of their unbinding can be larger than the curvature energy reduction on formation of QII phase from Lα at temperatures near the Lα/QII transition temperature (TQ). Using gu and elastic constant values typical of unsaturated PEs, we show that gu is sufficient to make TQ > TH for the latter lipids. Such systems would display direct Lα → HII transitions, and a QII phase might only form as a metastable phase upon cooling of the HII phase. The gu values for methylated PEs and PE/phosphatidylcholine mixtures are significantly smaller than those for PEs and increase TQ by only a few degrees, consistent with observations of these systems. This influence of gu also rationalizes the effect of some aqueous solutes to increase the rate of QII formation during temperature cycling of lipid dispersions. Finally, the results are relevant to protocols for determining the Gaussian curvature modulus, which substantially affects the energy of intermediates in membrane fusion and fission. Recently, two such methods were proposed based on measuring TQ and on measuring QII phase unit cell dimensions, respectively. In view of the effect of gu on TQ that we describe here, the latter method, which does not depend on the value of gu, is preferable. 相似文献
16.
Aline M. Pascoal Maria Carolina B. Di-Medeiros Karla A. Batista Maria Inês Gonçalves Leles Luciano Moraes Lião Kátia F. Fernandes 《Carbohydrate polymers》2013
In this study the pulp from Solanum lycocarpum fruits was used as raw material for extraction of starch, resulting in a yield of 51%. The starch granules were heterogeneous in size, presenting a conical appearance, very similar to a high-amylose cassava starch. The elemental analysis (CHNS) revealed 64.33% carbon, 7.16% hydrogen and 0.80% nitrogen. FT-IR spectroscopy showed characteristic peaks of polysaccharides and NMR analysis confirmed the presence of the α-anomer of d-glucose. The S. lycocarpum starch was characterized by high value of intrinsic viscosity (3515 mPa s) and estimated molecular weight around 645.69 kDa. Furthermore, this starch was classified as a B-type and high amylose content starch, presenting 34.66% of amylose and 38% crystallinity. Endothermic transition temperatures (To = 61.25 °C, Tp = 64.5 °C, Tc = 67.5 °C), gelatinization temperature (ΔT = 6.3 °C) ranges and enthalpy changes (ΔH = 13.21 J g−1) were accessed by DCS analysis. These results make the S. lycocarpum fruit a very promising source of starch for biotechnological applications. 相似文献
17.
Su–Su Xia An–Wei Yu Li–Dan Zhao Hui–Ying Zhang Wei–Hong Zheng Jin–Song Liu 《Journal of thermal biology》2013
Basal metabolic rate (BMR) is thought to be a major hub in the network of physiological mechanisms connecting life history traits. Evaporative water loss (EWL) is a physiological indicator that is widely used to measure water relations in inter- or intraspecific studies of birds in different environments. In this study, we examined the physiological responses of summer-acclimatized Hwamei Garrulax canorus to temperature by measuring their body temperature (Tb), metabolic rate (MR) and EWL at ambient temperatures (Ta) between 5 and 40 °C. Overall, we found that mean body temperature was 42.4 °C and average minimum thermal conductance (C) was 0.15 ml O2 g−1 h−1 °C−1 measured between 5 and 20 °C. The thermal neutral zone (TNZ) was 31.8–35.3 °C and BMR was 181.83 ml O2 h−1. Below the lower critical temperature, MR increased linearly with decreasing Ta according to the relationship: MR (ml O2 h−1)=266.59–2.66 Ta. At Tas above the upper critical temperature, MR increased with Ta according to the relationship: MR (ml O2 h−1)=−271.26+12.85 Ta. EWL increased with Ta according to the relationship: EWL (mg H2O h−1)=−19.16+12.64 Ta and exceeded metabolic water production at Ta>14.0 °C. The high Tb and thermal conductance, low BMR, narrow TNZ, and high evaporative water production/metabolic water production (EWP/MWP) ratio in the Hwamei are consistent with the idea that this species is adapted to warm, mesic climates, where metabolic thermogenesis and water conservation are not strong selective pressures. 相似文献
18.
Two extended metal atom chain (EMAC) compounds having a symmetrical Co36+ metal chain encapsulated by two N,N′-bis[(6′-pyrid-2″-yl)aminopyrid-2′yl]-bismethyl-2,6-diaminopyridinate (mpeptea) ligands have been prepared in good yield, and they have been structurally characterized by X-ray crystallography, magnetic and electrochemical measurements and spectroscopic techniques. For the EMAC [Co3(mpeptea)2]Cl2 two solvates have been crystallized. Anion exchange has also allowed isolation of [Co3(mpeptea)2](BPh4)2. In these three species the Co36+ units are cocooned within two polypyridine ligands having nine nitrogen atoms although only seven of these coordinate to the metal centers. The cations [Co3(mpeptea)2]2+ are similar and have Co ··· Co separations of ca. 2.3 Å at 213 K. These distances are consistent with partial bond formation between Co atoms. Electrochemical measurements show a unique one-electron oxidation process that differs from that in open chain species which show two reversible oxidation processes. At 300 K, the χT value is 7.32 emu K mol−1 but this value drops to 1.47 emu K mol−1 as the temperature is lowered to 2 K. The X-band EPR spectra for Co3(mpeptea)22+ show g values of 2.3 at room temperature. The magnetic behavior is quite different from that in compounds with open Co36+ units. A discussion is provided. 相似文献
19.
The glass transition and its related dynamics of myoglobin in water and in a water–glycerol mixture have been investigated by dielectric spectroscopy and differential scanning calorimetry (DSC). For all samples, the DSC measurements display a glass transition that extends over a large temperature range. Both the temperature of the transition and its broadness decrease rapidly with increasing amount of solvent in the system. The dielectric measurements show several dynamical processes, due to both protein and solvent relaxations, and in the case of pure water as solvent the main protein process (which most likely is due to conformational changes of the protein structure) exhibits a dynamic glass transition (i.e. reaches a relaxation time of 100 s) at about the same temperature as the calorimetric glass transition temperature Tg is found. This glass transition is most likely caused by the dynamic crossover and the associated vanishing of the α-relaxation of the main water relaxation, although it does not contribute to the calorimetric Tg. This is in contrast to myoglobin in water–glycerol, where the main solvent relaxation makes the strongest contribution to the calorimetric glass transition. For all samples it is clear that several proteins processes are involved in the calorimetric glass transition and the broadness of the transition depends on how much these different relaxations are separated in time. 相似文献
20.
Helmut Kovac Anton Stabentheiner Sigurd Schmaranzer 《Journal of insect physiology》2010,56(12):1834-1845
Foraging honeybees are subjected to considerable variations of microclimatic conditions challenging their thermoregulatory ability. Solar heat is a gain in the cold but may be a burden in the heat. We investigated the balancing of endothermic activity with radiative heat gain and physiological functions of water foraging Apis mellifera carnica honeybees in the whole range of ambient temperatures (Ta) and solar radiation they are likely to be exposed in their natural environment in Middle Europe.The mean thorax temperature (Tth) during foraging stays was regulated at a constantly high level (37.0-38.5 °C) in a broad range of Ta (3-30 °C). At warmer conditions (Ta = 30-39 °C) Tth increased to a maximal level of 45.3 °C. The endothermic temperature excess (difference of Tbody − Ta of living and dead bees) was used to assess the endogenously generated temperature elevation as a correlate of energy turnover. Up to a Ta of ∼30 °C bees used solar heat gain for a double purpose: to reduce energetic expenditure and to increase Tth by about 1-3 °C to improve force production of flight muscles. At higher Ta they exhibited cooling efforts to get rid of excess heat. A high Tth also allowed regulation of the head temperature high enough to guarantee proper function of the bees’ suction pump even at low Ta. This shortened the foraging stays and this way reduced energetic costs. With decreasing Ta bees also reduced arrival body weight and crop loading to do both minimize costs and optimize flight performance. 相似文献