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1.
Effects and molecular mechanisms of the biological action of weak and extremely weak magnetic fields
V. V. Novikov V. O. Ponomarev G. V. Novikov V. V. Kuvichkin E. V. Yablokova E. E. Fesenko 《Biophysics》2010,55(4):565-572
A number of effects of weak combined (static and alternating) magnetic fields with an alternating component of tens and hundreds
nT at a collinear static field of 42 μT, which is equivalent to the geomagnetic field, have been found: activation of fission
and regeneration of planarians Dugesia tigrina, inhibition of the growth of the Ehrlich ascites carcinoma in mice, stimulation of the production of the tumor necrosis factor
by macrophages, decrease in the protection of chromatin against the action of DNase 1, and enhancement of protein hydrolysis
in systems in vivo and in vitro. The frequency and amplitude ranges for the alternating component of weak combined magnetic
fields have been determined at which it affects various biological systems. Thus, the optimal amplitude at a frequency of
4.4 Hz is 100 nT (effective value); at a frequency of 16.5 Hz, the range of effective amplitudes is broader, 150–300 nT; and
at a frequency of 1 (0.5) Hz, it is 300 nT. The sum of close frequencies (e.g., 16 and 17 Hz) produces a similar biological
effect as the product of the modulating (0.5 Hz) and carrying frequencies (16.5 Hz), which is explained by the ratio A = A
0sinω1
t + A
0sinω2
t = 2A
0sin(ω1 + ω2)t/2cos(ω1–ω2)t/2. The efficiency of magnetic signals with pulsations (the sum of close frequencies) is more pronounced than that of sinusoidal
frequencies. These data may indicate the presence of several receptors of weak magnetic fields in biological systems and,
as a consequence, a higher efficiency of the effect at the simultaneous adjustment to these frequencies by the field. Even
with consideration of these facts, the mechanism of the biological action of weak combined magnetic fields remains still poorly
understood. 相似文献
2.
O. Buttelli H. Vandewalle J. C. Jouanin D. Seck H. Monod 《European journal of applied physiology and occupational physiology》1997,75(6):499-503
The kinetics of the torque-velocity (T-ω) relationship after aerobic exercise was studied to assess the effect of fatigue on the contractile properties of muscle.
A group of 13 subjects exercised until fatigued on a cycle ergometer, at an intensity which corresponded to 60% of their maximal
aerobic power for 50 min (MAP60%); ten subjects exercised until fatigued at 80% of their maximal aerobic power for 15 min
(MAP80%). Of the subjects 7 exercised at both intensities with at least a 1-week interval between sessions. Pedalling rate
was set at 60 rpm. The T-ω relationship was determined from the velocity data collected during all-out sprints against a 19 N · m braking torque on
the same ergometer, according to a method proposed previously. Maximal theoretical velocity (ω0) and maximal theoretical torque (T
0) were estimated by extrapolation of the linear T-ω relationship. Maximal power (P
max) was calculated from the values of T
0 and ω0 (P
max = 0.25 ω0 T
0). The T-ω relationships were determined before, immediately after and 5 and 10 min after the aerobic exercise. The kinetics of ω0, T
0 and P
max was assumed to express the effects of fatigue on the muscle contractile properties (maximal shortening velocity, maximal
muscle strength and maximal power). Immediately after exercise at MAP60% a 7.8% decrease in T
0 and 8.8% decrease in P
max was seen while the decrease in ω0 was nonsignificant, which suggested that P
max decreased in the main because of a loss in maximal muscle strength. In contrast, MAP80% induced a 8.1% decrease in ω0 and 12.8% decrease in P
max while the decrease in T
0 was nonsignificant, which suggested that the main cause of the decrease in P
max was probably a slowing of maximal shortening velocity. The short recovery time of the T-ω relationship suggests that the causes of the decrease of torque and velocity are processes which recover rapidly.
Accepted: 25 November 1996 相似文献
3.
John L. Stephenson 《Bulletin of mathematical biology》1960,22(1):1-17
The conditions under which the output,γ
b
(t), of a biological system is related to the input,γ
a
(t), by an integral equation of the typeγ
b
(t) = ∫
0
t
γ
a
(ω)w(t−ω)dω, where ω(t) is a transport functioncharacteristic of the system, are analyzed in detail. Methods of solving this type of integral equation are briefly discussed. The theory
is then applied to problems in tracer kinetics in which input and output are sums of exponentials, and explicit formulae,
which are applicable whether or not the pool is uniformly mixed, are derived for “turnover time” and “pool” size. 相似文献
4.
Background
We recently reported a highly unexpected positive correlation between the fixation probability of nonsynonymous mutations (estimated by ω) and neutral mutation rate (estimated by K s) in mammalian lineages. However, this positive correlation was observed for lineages with relatively long divergence time such as the human-mouse lineage, and was not found for very short lineages such as the human-chimpanzee lineage. It was previously unclear how to interpret this discrepancy. It may indicate that the positive correlation between ω and K s in long lineages is a false finding. Alternatively, it may reflect a biologically meaningful difference between various lineages. Finally, the lack of positive correlation in short lineages may be the result of methodological artifacts. 相似文献5.
Sally Bayer Claudia Birkemeyer Meike Ballschmiter 《Applied microbiology and biotechnology》2011,89(1):91-98
Several novel nitrilases were selected from metagenomic libraries using cinnamonitrile and a mixture of six different nitriles
as substrates. The nitrilase gene nit1 was expressed in Escherichia coli and the resulting protein was further examined concerning its biochemical properties. Nit1 turned out to be an aliphatic
nitrilase favoring dinitriles over mononitriles. Stereochemical analysis revealed that Nit1 converted the dinitrile 2-methylglutaronitrile
regioselectively. Hydrolysis at the ω-nitrile group of a dinitrile, such as catalyzed by Nit1, leads to ω-cyanocarboxylic
acids, which are important precursors for chemical and pharmaceutical products. Nit1 metabolized 2-methylglutaronitrile to
the corresponding ω-cyanocarboxylic acid 4-cyanopentanoic acid can be used for the production of the fine chemical 1,5-dimethyl-2-piperidone. 相似文献
6.
I. W. Richardson 《Bulletin of mathematical biology》1970,32(2):237-247
The Kedem-Katchalsky equation for the flow of a non-electrolyte through a homogeneous membrane is shown to be a first order
expansion of an exact integral of the Spiegler-Bearman-Kirkwood frictional equations under the assumption that the partial
frictional coefficients, ζ
ij
, are concentration independent. The equations are solved in terms of volume flow; there are no water-to-volume flow correction
terms for the permeability, ω, or the reflection coefficient, σ. The precision of the expansion depends upon the magnitude
of the water flow. The frictional coefficientsf
sm
andf
sw
are given as functions of the experimentally determined parameters ω and σ; the frictions, are shown to be independent ofL
p
. 相似文献
7.
The cytochrome c oxidase subunit 2 gene (COII) encodes a highly conserved protein that is directly responsible for the initial transfer of
electrons from cytochrome c to cytochrome c oxidase (COX) crucial to the production of ATP during cellular respiration. Despite its integral role in electron transport,
we have observed extensive intraspecific nucleotide and amino acid variation among 26 full-length COII sequences sampled from
seven populations of the marine copepod, Tigriopus californicus. Although intrapopulation divergence was virtually nonexistent, interpopulation divergence at the COII locus was nearly 20%
at the nucleotide level, including 38 nonsynonymous substitutions. Given the high degree of interaction between the cytochrome
c oxidase subunit 2 protein (COX2) and the nuclear-encoded subunits of COX and cytochrome c (CYC), we hypothesized that some codons in the COII gene are likely to be under positive selection in order to compensate
for amino acid substitutions in other subunits. Estimates of the ratio of nonsynonymous to synonymous substitution (ω), obtained
using a series of maximum likelihood models of codon substitution, indicated that the majority of codons in T. californicus COII are under strong purifying selection (ω << 1), while approximately 4% of the sites in this gene appear to evolve under
relaxed selective constraint (ω = 1). A branch-site maximum likelihood model identified three sites that may have experienced
positive selection within the central California sequence clade in our COII phylogeny; these results are consistent with previous
studies showing functional and fitness consequences among interpopulation hybrids between central and northern California
populations.
[Reviewing Editor: Dr. Willie Swanson] 相似文献
8.
Kurdyukov S Faust A Trenkamp S Bär S Franke R Efremova N Tietjen K Schreiber L Saedler H Yephremov A 《Planta》2006,224(2):315-329
In plants, extracellular matrix polymers built from polysaccharides and cuticular lipids have structural and protective functions. The cuticle is found to be ten times thinner in Arabidopsis thaliana (L.) Heynh than in many other plants, and there is evidence that it is unusual in having a high content of α-,ω-dicarboxylic fatty acids (FAs) in its polyesters. We designated the new organ fusion mutant hth-12 after it appeared to be allelic to adhesion of calyx edges (ace) and hothead (hth), upon molecular cloning of the gene by transposon tagging. This mutant is deficient in its ability to oxidize long-chain ω-hydroxy FAs to ω-oxo FAs, which results in leaf polyesters in decreased α-,ω-dicarboxylic FAs and increased ω-hydroxy FAs. These chemical phenotypes lead to disorder of the cuticle membrane structure in hth-12. ACE/HTH is a single-domain protein showing sequence similarity to long-chain FA ω-alcohol dehydrogenases from Candida species, and we hypothesize that it may catalyze the next step after cytochrome P450 FA ω-hydroxylases in the ω-oxidation pathway. We show that ACE/HTH is specifically expressed in epidermal cells. It appears very likely therefore that the changes in the amount of α-,ω-dicarboxylic FAs in hth-12 reflect the different composition of cuticular polyesters. The ACE/HTH gene is also expressed in root epidermal cells which do not form a polyester membrane on the exterior surface, thereby making it possible that the end products of the pathway, α-,ω-dicarboxylic FAs, are generally required for the cross-linking that ensures the integrity of the outer epidermal cell wall. 相似文献
9.
K. Hayakawa S. Tsujimura G. E. Napolitano S. Nakano M. Kumagai T. Nakajima C. Jiao 《Limnology》2002,3(1):29-35
The present study examined the fatty acid composition of Microcystis aeruginosa grown in a batch culture and that of Microcystis-dominated plankton collected in an experimental enclosure in a shallow, eutrophic embayment of Lake Biwa (Akanoi Bay). In
pure culture, we detected 16 : 0, 18 : 2ω6, 18 : 3ω3, 18 : 3ω6, and 18 : 4ω3 acids as major fatty acids of M. aeruginosa, with trace amounts of C20 polyunsaturated fatty acids. In both pure culture and the field enclosure, the ratio of total fatty acid weight to dry weight
decreased with decreasing availability of dissolved inorganic nitrogen. The ω3/ω6 ratios of C18 polyunsaturated fatty acids [(18 : 3ω3 + 18 : 4ω3)/(18 : 2ω6 + 18 : 3ω6)] varied greatly (range, 2–5) in response to the
changes in physical and chemical conditions for Microcystis growth. Most notably, the ω3/ω6 fatty acid ratios were significantly positively correlated with the growth rate of cells
in a batch culture. We suggest that the fatty acid composition is a useful indicator of the physiological state of Microcystis in freshwater lakes.
Received: March 2, 2001/ Accepted: December 19, 2001 相似文献
10.
An important criterion used to detect adaptive evolution in DNA sequence data is ωi > 1, where ωi is the ratio of nonsynonymous to synonymous substitution rates in lineage i. However, the evaluation of multiple ωi within a phylogenetic tree can easily inflate the statistical type I error rate. We developed two rigorous methods of analysis
that avoid this and other potential pitfalls. We applied these methods to four published examples of adaptive evolution. One
case was strongly supported by our reanalysis (abalone sperm lysin), and one was weakly supported (baboon α-globin), but two
examples (primate lysozyme and Antarctic fish β-globin) did not show significant evidence of adaptive evolution. Our first
method is a “bottom-up” hierarchical maximum likelihood approach, which (1) tests for significant heterogeneity in ω across
the phylogeny, (2) locates its source using a sequence of planned comparisons, and (3) tests homogeneous groups of ω for ω
> 1, using a modified level of significance that incorporates the pretesting. The second method is a “top-down” log-linear
analysis based on estimates of nonsynonymous and synonymous substitutions in pairs of lineages. The log-linear test is applied
to pairs of lineages joined at progressively deeper nodes. For each pair, the analysis simultaneously tests for adaptive evolution
(ω > 1), a shift in natural selection (ω1 ≠ω2), and unequal evolution rate (the relative rate test). In both tests, we emphasized that the criterion ω1 ≠ ω2 is an important additional indicator of a phylogenetic shift in the balance between natural selection and genetic drift between
two related lineages.
[Reviewing Editor: Dr. John Huelsenbeck] 相似文献
11.
ω-Transaminase (ω-TA) is an industrially important enzyme for production of chiral amines. About 20 (S)-specific ω-TAs known to date show remarkably similar substrate selectivity characterized by stringent steric constraint
precluding entry of a substituent larger than an ethyl group in the small binding pocket (S) and dual recognition of an aromatic
substituent as well as a carboxylate group in the large pocket (L). The strictly defined substrate selectivity of the available
ω-TAs remains a limiting factor in the production of structurally diverse chiral amines. In this work, we cloned, purified,
and characterized three new ω-TAs from Ochrobactrum anthropi, Acinetobacter baumannii, and Acetobacter pasteurianus that were identified by a BLASTP search using the previously studied ω-TA from Paracoccus denitrificans. All the new ω-TAs exhibited similar substrate specificity, which led us to explore whether the molecular determinants for
the substrate specificity are conserved among the ω-TAs. To this end, key active site residues were identified by docking
simulation using the X-ray structure of the ω-TA from Pseudomonas putida. We found that the dual recognition in the L pocket is ascribed to Tyr23, Phe88*, and Tyr152 for hydrophobic interaction
and Arg414 for recognition of a carboxylate group. In addition, the docking simulation indicates that Trp60 and Ile262 form
the S pocket where the substituent size up to an ethyl group turns out to be sterically allowed. The six key residues were
found to be essentially conserved among nine ω-TA sequences, underlying the molecular basis for the high similarity in the
substrate selectivity. 相似文献
12.
Price ER Staples JF Milligan CL Guglielmo CG 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2011,181(4):565-573
Birds primarily fuel migratory flights with fat, and the composition of that fat has the potential to affect overall lipid
oxidation rates. We measured the whole muscle lipid oxidation rates in extensor digitorum communis muscles from white-throated sparrows (Zonotrichia albicollis Gmelin) incubated for 20 min at 20°C with radiolabeled stearate (18:0), oleate (18:1ω9), or linoleate (18:2ω6). Lipid oxidation
rates were ~40% higher with linoleate than oleate (oleate: 36 ± 8.54 μmol CO2 g−1 h−1), and ~75% lower with stearate compared with oleate, indicating that maximal lipid oxidation rates can indeed be affected
by the type of fatty acid supplied to the muscle. Additionally, we investigated the activity of the mitochondrial fatty acid
transport-associated enzyme carnitine palmitoyl transferase (CPT) in pectoralis muscles of 5 bird species (Zonotrichia albicollis, Philomachus pugnax, Sturnus vulgaris, Taeniopygia guttata, Passer domesticus). Activity was measured in homogenized samples using various fatty acyl-CoA substrates (16:0, 16:1, 18:0, 18:1ω9, 18:2ω6,
18:3ω3, 18:3ω6, 20:0, 20:4ω6, 22:6ω3) in a spectrophotometric assay. CPT activity increased with the degree of unsaturation
and decreased with chain length. CPT activity did not differ between ω3 and ω6 isomers of 18:3, nor was the pattern of CPT
substrate preference different between captive white-throated sparrows in a migratory (i.e., displaying Zugunruhe) or non-migratory
state. These findings can explain previously observed differences in peak performance induced by dietary fat composition and
suggest that lipid supply is limiting to maximal exercise performance in birds. 相似文献
13.
Siristova L Luhovy R Sigler K Rezanka T 《Extremophiles : life under extreme conditions》2011,15(3):423-429
Two thermophilic strains belonging to Geobacillus stearothermophilus and Meiothermus ruber, which naturally do not synthesize ω-alicyclic fatty acids (ω-FAs) were cultivated with cyclopropyl, cyclobutyl, cyclopentyl
and cyclohexyl carboxylic acids. Gas chromatography–mass spectrometry analysis of fatty acid methyl and picolinyl esters showed
that both strains are able to synthesize ω-FAs when cultivated with the appropriate precursor. The incorporation of cyclic
acids influenced the whole FA composition as well as membrane fluidity. Membrane fluidity of intact cells was studied by measuring
the fluorescence polarisation of the probe l,6-diphenyl-1,3,5-hexatriene incorporated into membrane lipid bilayers. Cytoplasmic
membrane became more fluid with increasing content of ω-FAs. This is caused by considerable changes in lipid packing within
the membrane induced by the presence of ω-FAs not found in the natural environment of Geobacillus and Meiothermus strains. 相似文献
14.
Tae Hoo Yi Chang-Kyun Han Sathiyaraj Srinivasan Kang Jin Lee Myung Kyum Kim 《Journal of microbiology (Seoul, Korea)》2010,48(2):165-169
A Gram-negative, non-motile, non-spore-forming, small, orange, rod-shaped bacterium was isolated from soil in South Korea
and characterized to determine its taxonomic position. Phylogenetic analysis based on 16S rRNA gene sequence examination revealed
that strain PB323T belongs to the family Sphingomonadaceae. The highest degree of sequence similarity was found with Sphingomonas kaistensis PB56T (98.9%), followed by Sphingomonas astaxanthinifaciens TDMA-17T (98.3%). Chemotaxonomic characteristics (the G+C content of the genomic DNA 69.0 mol%, Q-10 quinone system, C18:1
ω7c/ω9t/ω12t, C16:1
ω7c/C15:0 iso 2OH, C17:1
ω6c, and C16:0 as the major fatty acids) corroborated assignment of strain PB323T to the genus Sphingomonas. Results of physiological and biochemical tests clearly demonstrate that strain PB323T represents a distinct species and support its affiliation with the genus Sphingomonas. Based on these data, PB323T (=KCTC 12341T =JCM 16603T =KEMB 9004-003T) should be classified as a type strain of a novel species, for which the name Sphingomonas humi sp. nov. is proposed. 相似文献
15.
Dynamical models of two coupled biological oscillators interpret the detuning term as an arithmetic difference between the
uncoupled frequencies, Δω= (ω1−ω2). This Δω interpretation of detuning was addressed in four experiments in which human subjects oscillated pendulums in their
right and left hands in 1 : 1 frequency locking in antiphase (Experiments 1–3) or inphase (Experiment 4). Differences between
the uncoupled frequencies were manipulated through differences in the equivalent simple pendulum lengths, and the effects
of this manipulation on the detuning of relative phase from π or 0 and the standard deviation of relative phase SDφ were measured.
In Experiment 1, the same values of ω
i
were satisfied by several different physical configurations. The experiment confirmed that the detuning term is related strictly
to the uncoupled frequencies rather than to other physical characteristics of the oscillators. Experiments 2, 3 and 4 showed,
however, that the particular dependency of fixed point drift and SDφ on Δω depends on the particulars of ω1 and ω2. With variations in Δω brought about by different ω1 and ω2 that always formed a constant ratio, fixed point drift related inversely to Δω, and SDφ varied with Δω in ways that depended
on the magnitude of the constant ratio. These outcomes do not conform to expectations from models of coordination dynamics
that interpret detuning as (ω1−ω2).
Received: 18 October 1993/Accepted in revised form: 2 December 1994 相似文献
16.
ω3-fatty acid desaturase and Δ12-fatty acid desaturase of Pichia pastoris with distinguishable regioselectivity and high degree of sequence similarity were chosen for regioselectivity research. Chimeras
were constructed in which Histidine-rich boxes 1, 2 and the carboxyl terminal region of ω3-fatty acid desaturase were replaced with corresponding region of Δ12-fatty acid desaturase. The replacement was found to result in a change of regioselectivity from ωy to x + 3 by functionally characterizing these chimeric enzymes in Saccharomyces cerevisae strain INVScI. Using site-directed mutagenesis, we further demonstrated that seven conserved amino acids of ω3-fatty acid desaturase within the first two Histidine-rich regions are responsible for the regioselectivity switch. Therefore,
the regioselectivity of fatty acid desaturases may be better understood by investigating the evolutionary relationships of
different fatty acid desaturases.
Dongsheng Wei is the partake of first-author’s profits. 相似文献
17.
We have studied how disturbance by ploughing and rotavation affects the carbon (C) flow to arbuscular mycorrhizal (AM) fungi
in a dry, semi-natural grassland. AM fungal biomass was estimated using the indicator neutral lipid fatty acid (NLFA) 16:1ω5,
and saprotrophic fungal biomass using NLFA 18:2ω6,9. We labeled vegetation plots with 13CO2 and studied the C flow to the signature fatty acids as well as uptake and allocation in plants. We found that AM fungal biomass
in roots and soil decreased with disturbance, while saprotrophic fungal biomass in soil was not influenced by disturbance.
Rotavation decreased the 13C enrichment in NLFA 16:1ω5 in soil, but 13C enrichment in the AM fungal indicator NLFA 16:1ω5 in roots or soil was not influenced by any other disturbance. In roots,
13C enrichment was consistently higher in NLFA 16:1ω5 than in crude root material. Grasses (mainly Festuca brevipila) decreased as a result of disturbance, while non-mycorrhizal annual forbs increased. This decreases the potential for mycorrhizal
C sequestration and may have been the main reason for the reduced mycorrhizal C allocation found in disturbed plots. Disturbance
decreased the soil ammonium content but did not change the pH, nitrate or phosphate availability. The overall effect of disturbance
on C allocation was that more of the C in AM fungal mycelium was directed to the external phase. Furthermore, the functional
identity of the plants seemed to play a minor role in the C cycle as no differences were seen between different groups, although
annuals contained less AM fungi than the other groups. 相似文献
18.
19.
S. Kandel V. Sauveplane A. Olry L. Diss I. Benveniste F. Pinot 《Phytochemistry Reviews》2006,5(2-3):359-372
In plants, hydroxy-fatty acid production is mainly the result of enzymatic reactions catalyzed by cytochrome P450 dependent fatty acid hydroxylases. One can distinguish ω-hydroxylases that catalyze the hydroxylation of the terminal methyl of aliphatics acids (ω position) and sub-terminal or in-chain hydroxylases that oxidize carbons in the chain (ω-n position). Since both types of enzymes were discovered about three decades ago, the majority of investigations have focused on the CYP94 and CYP86 families, which mediate ω-hydroxylations. The activities of ω-hydroxylases in cutin synthesis have been clearly established, but the studies of LCR (LACERATA) and att1 (aberrant induction of type three genes), which are the first Arabidopsis thaliana mutants with alterations in coding sequences of CYP86A8 and CYP86A2, show that these types of ω-hydroxylases can be involved in many aspects of plant development. The existence of different ω-hydroxylases in plants with distinct regulation patterns suggests that these enzymes mediate diverse biological processes. Much less information concerning in-chain hydroxylases is available despite the fact that they were initially reported along with ω-hydroxylases. This lack of information might be explained by the very few examples of sub-terminal hydroxy-fatty acids described in plants. We present here the best characterized fatty acid hydroxylases and we discuss their possible roles in plant defense and development, fatty acid catabolism, plant reproduction and detoxification. 相似文献
20.
Following our established theoretical model to deal with the second-harmonic generation (SHG) excited by a linearly polarized
focused beam in type I collagen, in this paper, we further quantitatively characterize the differences between SHG emissions
in type I collagen excited by collimated and focused beams. The effects of the linear polarization angle (α) and the fibril polarity characterized by the hyperpolarizability ratio ρ on SHG emission has been compared under collimated and focused beam excitation, respectively. In particular, SHG emission
components along the i axis ( I2w,i )\left( {I_{2\omega {,}i} } \right) (i = x,y,z), the induced SHG emission deviation angle γ
ij
, and the detected SHG signals (I
2ω,ij
) in the ij plane by rotating the applied polarizer angle φ
ij
have been investigated (i = x, x, y; j = y, z, z). Results show that under our simulation model, SHG emission in the xy plane, such as I
2ω,x
,I
2ω,y
,γ
xy
and I
2ω,xy
varying as polarization angle (α) under collimated and focused light, presents no significant difference. The reverse of the fibril polarity has induced great
impact on I
2ω,x
,γ
xy
and I
2ω,xy
in both collimated and focused light. I
2ω,x
and γ
xy
show similarity, but I
2ω,xy
at α = 30° demonstrates a slight difference in focused light to that in collimated light. Under focused light, the reverse of
fibril polarity causes obvious changes of the collected SHG intensity I
2ω,xz
and I
2ω,yz
at a special polarization angle α = 60° and γ
xz
, γ
yz
along α. 相似文献