Larch (Larix kaempferi) xylem parenchyma cells respond to subfreezing temperature by deep supercooling

In previous studies, xylem parenchyma cells (XPCs) in the boreal softwood species larch, which has thick and rigid walls similar to those of XPCs in boreal hardwood species, were shown to respond to subfreezing temperature by deep supercooling during summer but change their freezing behavior to extracellular freezing during winter. In this study, we re-examined freezing behavior of XPCs in larch by observation of deep etching of frozen samples as well as observation of re-warmed samples after freezing using a cryo-scanning electron microscope. The results showed that XPCs in larch adapts to subfreezing temperature by deep supercooling throughout all seasons. Such freezing behavior is the same as that of XPCs in boreal hardwood species.     

Microscopic characterization of tension wood cell walls of Japanese beech (Fagus crenata) treated with ionic liquids

Tension wood that is an abnormal part formed in angiosperms has been barely used for wood industry. In this study, to utilize the tension wood effectively by means of liquefaction using ionic liquid, we performed morphological and topochemical determination of the changes in tension wood of Japanese beech (Fagus crenata) during ionic liquid treatment at the cellular level using light microscopy, scanning electron microscopy and confocal Raman microscopy. Ionic liquid treatment induced cell wall swelling in tension wood. Changes in the tissue morphology treated with ionic liquids were different between normal wood and tension wood, moreover the types of ionic liquids. The ionic liquid 1-ethyl-3-methylimidazolium chloride liquefied gelatinous layers rapidly, whereas 1-ethylpyridinium bromide liquefied slowly but delignified selectively. These novel insights into the deconstruction behavior of tension wood cell walls during ionic liquid treatment provide better understanding of the liquefaction mechanism. The obtained knowledge will contribute to development of an effective chemical processing of tension wood using ionic liquids and lead to efficient use of wood resources.     

Cryo-scanning electron microscopic study on freezing behavior of xylem ray parenchyma cells in hardwood species

Differential thermal analysis (DTA) has indicated that xylem ray parenchyma cells (XRPCs) of hardwood species adapt to freezing of apoplastic water either by deep supercooling or by extracellular freezing, depending upon the species. DTA studies indicated that moderately cold hardy hardwood species exhibiting deep supercooling in the XRPCs were limited in latitudinal distribution within the −40°C isotherm, while very hardy hardwood species exhibiting extracellular freezing could distribute in colder areas beyond the −40°C isotherm. Predictions based on the results of DTA, however, indicate that XRPCs exhibiting extracellular freezing may appear not only in very hardy woody species native to cold areas beyond the −40°C isotherm but also in less hardy hardwood species native to tropical and subtropical zones as well as in a small number of moderately hardy hardwood species native to warm temperate zones. Cryo-scanning electron microscopic (cryo-SEM) studies on the freezing behavior of XRPCs have revealed some errors in DTA. These errors are originated mainly due to the overlap between exotherms produced by freezing of water in apoplastic spaces (high temperature exotherms, HTEs) and exotherms produced by freezing of intracellular water of XRPCs by breakdown of deep supercooling (low temperature exotherms, LTEs), as well as to the shortage of LTEs produced by intracellular freezing of XRPCs. In addition, DTA results are significantly affected by cooling rates employed. Further, cryo-SEM observations, which revealed the true freezing behavior of XRPCs, changed the previous knowledge of freezing behavior of XRPCs that had been obtained by freeze-substitution and transmission electron microscopic studies. Cryo-SEM results, in association with results obtained from DTA that were reconfirmed or changed by observation using a cryo-SEM, revealed a clear tendency of the freezing behavior of XRPCs in hardwood species to change with changes in the temperature in the growing conditions, including both latitudinal and seasonal temperature changes. In latitudinal temperature changes, XRPCs in less hardy hardwood species native to tropical and subtropical zones exhibited deep supercooling to −10°C, XRPCs in moderately hardy hardwood species native to temperate zones exhibited a gradual increase in the supercooling ability to −40°C from warm toward cool temperate zones, and XRPCs in very hardy hardwood species native to boreal forests exhibited extracellular freezing via an intermediate form of freezing behavior between deep supercooling and extracellular freezing. In seasonal temperature changes, XRPCs in hardwood species native to temperate zones changed their supercooling ability from a relatively low degree in summer to a high degree in winter. XRPCs in hardwood species native to boreal forests changed their freezing behavior from deep supercooling to −10°C in summer to extracellular freezing in winter. These results indicate that the freezing behavior of XRPCs in hardwood species tends to shift gradually from supercooling of −10°C, to a gradual increase in the deep supercooling ability to −40°C or less, and finally to extracellular freezing as a result of cold acclimation in response to both latitudinal and seasonal temperature changes. It is thought that these temperature-dependent changes in the freezing behavior of XRPCs in hardwood species are mainly controlled by changes in cell wall properties, although no distinct changes were detected by electron microscopic observations in cell wall organization between hardwood species or between seasons. Evidence of temperature-dependent changes in the freezing behavior of XRPCs in hardwood species provided by the results of studies using a cryo-SEM has indicated the need for further investigation to clarify cold acclimation-induced cell wall changes at the sub-electron microscopic level in order to understand the mechanisms of freezing adaptation.     

A dual 13C and 15N long-term labelling technique to investigate uptake and translocation of C and N in beech (Fagus sylvatica L.)

A continuous dual 13CO2 and 15NH4(15)NO3 labelling experimental set-up is presented that was used to investigate the C and N uptake and allocation within 3-year old beech (Fagus sylvatica L.) during one growing season. The C and N allocation pattern was determined after six, twelve and eighteen weeks of growth. The carbon uptake was distinctly different in the three phases examined: The first six weeks after budbreak were dedicated to leaf growth with a R/S (root to shoot) ratio of 0.14 for the new carbon. The second growth phase showed a balanced R/S ratio of C allocation and after week 13, the root compartment was the main carbon sink (R/S = 6.97). Nitrogen allocation was more basipetal as compared to carbon. In the second growth phase, R/S of Nnew was 5.57 but fell to 3.54 for the third growth phase probably due to formation of reserves in buds and stem.     

Role of surface reconstructions in (111) silicon fracture

The (111) cleavage in crystalline silicon was investigated by hybrid quantum/classical atomistic simulations showing that its remarkable stability is largely due to asymmetric π-bonded reconstructions of the cleavage surfaces created by the advancing crack front. Further simulations show that the same reconstructions can induce an asymmetric dynamical response to added shear stress components. This explains why [211] upward steps are much more common than [211] downward steps on (111) cleavage surfaces, while "zigzag" cleavage with alternated (111) and (111) facets will still occur in crystal samples fractured under [110] uniaxial loading.     

Role of sub-surface oxygen in Cu(100) oxidation

Density functional theory (DFT) calculations are used to investigate the role of sub-surface oxygen in Cu(100) oxidation. We find that the presence of sub-surface oxygen atoms causes the top copper layer of the missing-row reconstructed surface to rise by 1.7 Å compared to the bare surface. This prediction compares well to an earlier scanning tunneling microscopy measurement of 1.8 Å [Lampimaki et al. Journal of Chemical Physics 126 (2007) 034703]. When the missing-row reconstructed surface is exposed to an additional oxygen molecule, surface restructuring that leads to oxide-like structures is only observed when sub-surface oxygen is present. The oxide-like nature of these structures is confirmed through structural, Bader, and electron density of states analyses. These findings, combined with our previous DFT results that predicted low energy barriers for the embedment of oxygen atoms into the sub-surface [Lee and McGaughey, Surface Science 603 (2009) 3404], demonstrate the key role played by sub-surface oxygen in Cu(100) oxidation.     

Role of strontium in oxide epitaxy on silicon (001)

Epitaxial oxide-Si heterostructures, which integrate the functionality of crystalline oxides with Si technology, are made possible by a submonolayer of Sr deposited on Si (001). We find by electron diffraction studies using single termination Si wafers that this Sr submonolayer replaces the top layer of Si when deposited at 650 degrees C. Supported by first-principles calculations, we propose a model for the reaction dynamics of Sr on the Si surface and its effect on oxide epitaxy. This model predicts, and we experimentally confirm, an unexplored 25 degrees C pathway to crystalline oxide epitaxy on Si.     

Calibration methods and avoidance of errors in measurement of intracellular pH (pHcyt) using the indicator bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF) in human platelets

Determinations of pH_cyt in suspensions of human platelets using BCECF [bis(carboxyethyl)-5(6)-carboxyfluorescein] can be seriously biased by leakage of the fluorescent indicator. Two methods (pH jump and Mn²⁺) are presented for determining the fraction of external indicator (B _ext) and eliminating this error. Both methods rely on rapid perturbations (pH jump or Mn²⁺ addition), which affect the fluorescence of the external dye immediately and the intracellular dye more slowly. Identical values ofB _ext are reported. Failure to correct for dye leakage can result in overestimation of pH_cyt by as much as 0.4 unit at physiological external pH (pH_ext). Two methods of calibration of the cytoplasmic signal were compared after correcting forB _ext: the digitonin lysis method and the nigericin calibration method. In the digitonin method the dye is released at the end of the experiment and the dependence of its fluorescence is determined as a function of pH. The method assumes that the fluorescence and titration characteristics of the dye in the cytoplasm are not different from those in solution. It gives pH_cyt=6.75±0.07 for pH_ext=7.3. In the nigericin method, 150 mM external K⁺ and 10 M nigericin are used for the purpose of setting pH_cyt=pH_ext to accomplish anin situ calibration. The method was complicated by extra leakage induced by nigericin. Assuming that the ionophore could equilibrate pH in the alkaline range, the fluorescence of the anionic form of BCECF in the cytoplasm would be 15% lower than in solution and pH_cyt would be 0.3 unit higher than presented above. A number of observations favor the digitonin lysis method of calibration. The fluorescence polarization of BCECF in platelets is small and indistinguishable from that in solution (0.000±0.022). The spectrofluorimetric characteristics of the intracellular dye are identical to those in solution (150 mM NaCl or KCl). There was no evidence for self-quenching or binding to cellular elements for cytoplasmic BCECF concentrations up to 1.8 mM. The following agents are capable of introducing error: (1) the Na⁺ substituteN-methyl-d-glucamine doubles theK _d and decreases by 13% the F _max of BCECF; (2) the Na⁺/H⁺ exchange inhibitor amiloride quenches BCECF fluorescence and is intrinsically fluorescent; and (3) bovine serum albumin (used to remove nigericin) quenches external BCECF with kinetics mimicking acidification of the cytoplasm.     

Role ofΔ(1232) in pion condensation in16O

We investigate the effect of Δ(1232) in pion condensation in¹⁶O within a model where the spins of all protons are oriented in one direction and those of neutrons in opposite direction. Both the π and the ρ exchange interactions have been considered. The effect of the Δ(1232) is found to be important.     

The Role of Entropy in Construct Specification Equations (CSE) to Improve the Validity of Memory Tests

Commonly used rating scales and tests have been found lacking reliability and validity, for example in neurodegenerative diseases studies, owing to not making recourse to the inherent ordinality of human responses, nor acknowledging the separability of person ability and item difficulty parameters according to the well-known Rasch model. Here, we adopt an information theory approach, particularly extending deployment of the classic Brillouin entropy expression when explaining the difficulty of recalling non-verbal sequences in memory tests (i.e., Corsi Block Test and Digit Span Test): a more ordered task, of less entropy, will generally be easier to perform. Construct specification equations (CSEs) as a part of a methodological development, with entropy-based variables dominating, are found experimentally to explain (r =R2 = 0.98) and predict the construct of task difficulty for short-term memory tests using data from the NeuroMET (n = 88) and Gothenburg MCI (n = 257) studies. We propose entropy-based equivalence criteria, whereby different tasks (in the form of items) from different tests can be combined, enabling new memory tests to be formed by choosing a bespoke selection of items, leading to more efficient testing, improved reliability (reduced uncertainties) and validity. This provides opportunities for more practical and accurate measurement in clinical practice, research and trials.     

Role of composite MnO2 cathode on electrochemical cells based on polymer electrolyte (PEO/NaClO3)

Thin-film sodium-ion-conducting polymer electrolyte based on polyethylene oxide (PEO) system was prepared by solvent casting method. The thin-film electrolytes were characterized by X-ray diffraction (XRD), infrared (IR), cyclic voltammetry (CV) and alternating current conductivity, and Wagner’s polarization method. The complexation of salt with PEO was confirmed by XRD and IR studies. The charge transport of these electrolytes is mainly due to ions, which was confirmed by the transference number experiment. The conductivity studies show that the conductivity value of PEO/NaClO₃ complex increases with the increase of temperature as well as the addition of low molecular weight polyethylene glycol, dimethyl formamide, and propylene carbonate. The electrolyte stability and cell reversibility were analyzed by CV studies. Electrochemical cells have been fabricated with a common cell configuration Na|electrolyte|(MnO₂ + I₂ + C + electrolyte), and their discharge characteristic studies were made through a load 100 kΩ at room temperature. The measured open circuit voltage ranges from 2.80 to 2.54 V with short circuit current ranges from 667 to 1,000 μA and several other cell parameters were evaluated. Finally, the merit of the composite cathode is found with the comparison of the MnO₂ cathode.     

Role of manganese in ferromagnetic (Al,Mn)N films

We have studied the (Al,Mn)N films grown by plasma-enhanced molecular beam epitaxy via Raman spectroscopy to verify how Mn atoms were incorporated into AlN lattice. In Raman spectra of (Al,Mn)N, the frequency of E₂ (high) mode blueshifts. Together with XRD results, the strain calculations support the existence of the substitutional dopant. Also, an additional peak, attributed to local vibrational mode of Mn, coincides with the calculated phonon frequency on the basis of a simple model. The Raman results reveal that Mn atoms replace Al atoms at the substitutional sites in the lattice. The (Al,Mn)N films were found to exhibit insulating characteristics and ferromagnetic ordering above room temperature. These results suggest that the ferromagnetism in the (Al,Mn)N films is due to the intrinsic nature originating from the substitutional Mn within (Al,Mn)N.     

Role of long range interaction in oxygen superstructure formation on Cu(001) and Ni(001)

On the basis of electronic structure calculations, we show that the long range Coulomb interaction provides the driving mechanism for oxygen overlayer formation on Cu(001). We illustrate that this interaction in the precursor c(2 x 2) phase induces a missing row reconstruction of Cu(001), and leads to the (2sqrt[2] x sqrt[2])R45 degrees O structure, which has strong covalent pO-dCu coupling. For the c(2 x 2)O overlayer on Ni(001) and Cu(001), we show that pO-dNi bonding is larger than pO-dCu and serves to neutralize the perturbation of the Coulomb interaction induced by the O overlayer. Consequently, c(2 x 2)O/Ni(001)) is stable while c(2 x 2)O/Cu(001) exists only in limited environments.     

Role of interdimer interactions in NH3 dissociation on si(100)-(2x1)

The dissociation of NH3 on Si(100)-(2x1) is investigated by a combination of infrared absorption spectroscopy and density functional cluster calculations, revealing that this reaction is governed by a complex set of interdimer interactions involving both bare and adsorbate-covered Si dimers. We propose that such adsorbate-induced changes in the electronic structure of neighboring dimers may have general implications for controlling the two-dimensional ordering of reactions on the dimerized Si(100) surface.     

Role of Au(+) in supporting and activating Au(7) on TiO(2)(110)

The adhesion properties and catalytic activity of rutile TiO(2)(110)-supported Au(7) nanoclusters in different oxidation states are investigated by means of density functional theory. The calculations cover both surface science conditions of reduced TiO(2) and real catalyst conditions of oxidized (alkaline) TiO(2) supports. Large adhesion energies of Au(7) are found only when modeling real catalysts where the cluster becomes cationic with Au(+) ions in Au-O or Au-OH bonds. The full catalytic cycle for oxidation of CO by O(2) over Au(7) on alkaline TiO(2)(110) is calculated and found to involve only small activation barriers. In the presence of the CO reductant, the Au(+) sites are capable of cycling between bonding of atomic and molecular oxygen. We confirm our findings by comparison of calculated and experimental infrared stretch frequency data for adsorbed CO.