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1.
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
2.
The study comprises a data set of CTD, optical properties—K
0(PAR), c
p, a(PAR), b(PAR)—and optical constituents—Chl a, SPM, CDOM—from 72 shelf and off-shelf stations in the Faroe Islands (62°N, 7°W) North East Atlantic, in early spring 2005.
Results showed that shelf waters surrounding the islands were cold and low saline, whereas off-shelf waters were warmer (~1°C)
and more saline (~0.05) PSU. A pronounced oceanographic front separated the two waters, and diffuse light attenuation K
0(PAR), beam attenuation c
p, Chl a, absorption a(PAR), and scattering coefficient b(PAR) were all significantly higher on the shelf. Analyses showed that off-shelf light attenuation K
0(PAR) was governed by Chl a, shown by a high (r
2 = 0.64) Chl a–K
0(PAR) correlation, whereas light attenuation on the shelf was governed by both Chl a, SPM, and CDOM in combination. A Chl a specific diffuse attenuation coefficient
K0* ( \textPAR ) K_{0}^{*} \left( {\text{PAR}} \right) of 0.056 (m2 mg−1 Chl a) and a Chl a specific beam attenuation (
c\textp* c_{\text{p}}^{*} ) of 0.27 (m2 mg−1 Chl a) coefficients were derived for the off-shelf. It is pointed out that Chl a is the single variable that changes over time as no rivers with high SPM and CDOM enter the shelf area. Data were obtained
in early spring, and Chl a concentrations were low ~0.5 mg Chl a m−3. Spring bloom Chl a are about 10 mg Chl a m−3 and estimations showed that shelf K
0(PAR) will increase about 5 times and beam attenuation about 10 times. The Faroe Islands shelf–off-shelf waters is a clear
example where physical conditions maintain some clear differences in optical properties and optical constituents. The complete
data set is enclosed. 相似文献
3.
Experimental study of a glow discharge with electrostatic confinement of electrons is carried out in the vacuum chamber volume
V ≈ 0.12 m3 of a technological system “Bulat-6” in argon pressure range 0.005–5 Pa. The chamber is used as a hollow cathode of the discharge
with the inner surface area S ≈ 1.5 m2. It is equipped with two feedthroughs, which make it possible to immerse in the discharge plasma interchangeable anodes with
surface area S
a
ranging from ∼0.001 to ∼0.1 m2, as well as floating electrodes isolated from both the chamber and the anode. Dependences of the cathode fall U
c
= 0.4−3 kV on the pressure p at a constant discharge current in the range I = 0.2−2 A proved that aperture of the electron escape out of the electrostatic trap is equal to the sum S
o = S
a
+ S
f
of the anode surface S
a
and the floating electrode surface S
f
. The sum S
o defines the lower limit p
o of the pressure range, in which U
c
is independent of p. At p < p
o the cathode fall U
c
grows up dramatically, when the pressure decreases, and the pressure p tends to the limit p
ex, which is in fact the discharge extinction pressure. At p ≈ p
ex electrons emitted by the cathode and the first generation of fast electrons produced in the cathode sheath spend almost all
their energy up to 3 keV on heating the anode and the floating electrode up to 600–800°C and higher. In this case the gas
in the chamber is being ionized by the next generations of electrons produced in the cathode sheath, their energy being one
order of magnitude lower. When S
a
< (2m/M)1/2
S, where m is the electron mass and M is the ion mass, the anode may be additionally heated by plasma electrons accelerated by the anode fall of potential U
a
up to 0.5 kV. 相似文献
4.
The differences in pigment levels, photosynthetic activity and the chlorophyll fluorescence decrease ratio R
Fd (as indicator of photosynthetic rates) of green sun and shade leaves of three broadleaf trees (Platanus acerifolia Willd., Populus alba L., Tilia cordata Mill.) were compared. Sun leaves were characterized by higher levels of total chlorophylls a + b and total carotenoids x + c as well as higher values for the weight ratio chlorophyll (Chl) a/b (sun leaves 3.23–3.45; shade leaves: 2.74–2.81), and lower values for the ratio chlorophylls to carotenoids (a + b)/(x + c) (with 4.44–4.70 in sun leaves and 5.04–5.72 in shade leaves). Sun leaves exhibited higher photosynthetic rates P
N on a leaf area basis (mean of 9.1–10.1 μmol CO2 m−2 s−1) and Chl basis, which correlated well with the higher values of stomatal conductance G
s (range 105–180 mmol m−2 s−1), as compared to shade leaves (G
s range 25–77 mmol m−2 s−1; P
N: 3.2–3.7 μmol CO2 m−2 s−1). The higher photosynthetic rates could also be detected via imaging the Chl fluorescence decrease ratio R
Fd, which possessed higher values in sun leaves (2.8–3.0) as compared to shade leaves (1.4–1.8). In addition, via R
Fd images it was shown that the photosynthetic activity of the leaves of all trees exhibits a large heterogeneity across the
leaf area, and in general to a higher extent in sun leaves than in shade leaves. 相似文献
5.
Ferdinand Schanz 《Hydrobiologia》1986,134(2):183-192
Spectral light attenuation, from the surface to 20 m, was followed on 15 sunny days and compared with the vertical phytoplankton
distribution. The most penetrating wavelengths lie between 565 and 590 nm. High phytoplankton density causes a rapid loss
of blue light with depth. Consequently the yellow and red regions of the spectrum contain a relatively high proportion of
the light energy present at a particular depth. The vertical attenuation coefficients of monochromatic light Kd(λ) in the 400 to 700 nm region are influenced significantly by the phytoplankton biomass. The specific light attenuation
coefficient for chlorophyll a (kc) is highest below 550 nm (e.g. 450 nm, surface layer: kc = 0.027 m2 · mg−1, n = 14; lowermost layer: kc = 0.044 m2 · mg−1, n = 9). 相似文献
6.
Teresa Mancilla-Percino José Correa-Basurto José Trujillo-Ferrara Fernando R. Ramos-Morales Mario E. Acosta Hernández Jesús S. Cruz-Sánchez Margarita Saavedra-Vélez 《Journal of molecular modeling》2010,16(8):1377-1382
Two series of isoindolines 1(a–g) and 2(a–g) were found by docking calculations to be possible L-type Ca2+ channel (LCC) blockers. The theoretical 3-D model of the outer vestibule and the selective filter of the LCC was provided
by Professor Lipkind; this model consists of transmembrane segments S5 and S6 and P-loops contributed by each of four repeats
(I, II, III, and IV) of Cav 1.2. Therefore, two well-known LCC blockers, nifedipine 3 and (R)-ethosuccinimide 4 were also evaluated, and their binding sites on the LCC were identified and compared with those obtained for 1(a–g) and 2(a–g). Analysis of the results shows that the target compounds tested probably could be LCC blockers, since they interact with
or near the glutamic acid residues Glu393, Glu736, Glu1145 and Glu1446 (the EEEE locus), which belong to the LCC selectivity
region. The ∆G values for all of the Ca2+ channel ligands are between−10.78 and −3.67 (kcal mol−1), showing that LCC-1b, -1e and -1f complexes are more stable than the other compounds tested. Therefore, theoretically calculated dissociation constants K
d (μM) were obtained for all compounds. Comparing these values reveals that compounds 1b (0.0244 μM), 1e (0.0176 μM) and 1f (0.0125 μM) exhibit more affinity for the LCC than the other compounds. This screening shows that the two series of isoindolines
probably could act as LCC blockers. 相似文献
7.
Due to anthropogenic influences, solar UV-B irradiance at the earth’s surface is increasing. To determine the effects of enhanced
UV-B radiation on photosynthetic characteristics of Prunus dulcis, two-year-old seedlings of the species were submitted to four levels of UV-B stress, namely 0 (UV-Bc), 4.42 (UV-B1), 7.32 (UV-B2) and 9.36 (UV-B3) kJ m−2 d−1. Effects of UV-B stress on a range of chlorophyll (Chl) fluorescence parameters (FPs), Chl contents and photosynthetic gas-exchange
parameters were investigated. UV-B stress promoted an increase in minimal fluorescence of dark-adapted state (F0) and F0/Fm, and a decrease in variable fluorescence (Fv, Fv/Fm, Fv/F0 and F0/Fm) due to its adverse effects on photosystem II (PSII) activity. No significant change was observed for maximal fluorescence
of dark-adapted state (Fm). Enhanced UV-B radiation caused a significant inhibition of net photosynthetic rate (P
N) at UV-B2 and UV-B3 levels and this was accompanied by a reduction in stomatal conductance (g
s) and transpiration rate (E). The contents of Chl a, b, and total Chl content (a+b) were also significantly reduced at increased UV-B stress. In general, adverse UV-B effects became significant at the highest
tested radiation dose 9.36 kJ m−2 d−1. The most sensitive indicators for UV-B stress were Fv/F0, Chl a content and P
N. Significant P<0.05 alteration in these parameters was found indicating the drastic effect of UV-B radiation on P. dulcis. 相似文献
8.
Michael J. Webster Timothy P. Scheett Matthew R. Doyle Matthew Branz 《European journal of applied physiology and occupational physiology》1997,75(6):520-524
The purpose of this study was to investigate the effect of a thiamin derivative, thiamin tetrahydrofurfuryl disulfide (TTFD),
on oxygen uptake (˙VO2), lactate accumulation and cycling performance during exercise to exhaustion. Using a randomized, double-blind, cross-over
design with a 10-day washout between trials, 14 subjects ingested either 1 g · day−1 of TTFD or a placebo (PL) for 4 days. On day 3, subjects performed a progressive exercise test to exhaustion on a cycle ergometer
for the determination of ˙VO2submax, ˙VO2peak, lactate concentration ([La− ]), lactate threshold (ThLa) and heart rate ( f
c). On day 4, subjects performed a maximal 2000-m time trial on a cycle ergometer. A one-way analysis of variance (ANOVA) with
repeated measures was used to determine significant differences between trials. There were no significant differences detected
between trials for serial measures of ˙VO2submax, [La−] or f
c. Likewise, ˙VO2peak [PL 4.06 (0.19) TTFD 4.12 (0.19) l · min−1, P = 0.83], ThLa [PL 2.47 (0.17), TTFD 2.43 (0.16) l · min−1, P = 0.86] and 2000-m performance time [PL 204.5 (5.5), TTFD 200.9 (4.3) s, P = 0.61] were not significantly different between trials. The results of this study suggest that thiamin derivative supplementation
does not influence high-intensity exercise performance.
Accepted: 19 December 1996 相似文献
9.
Zhang JG Feng LN Shu YJ Zhang SW Zhang TL Yang L Wu M 《Journal of molecular modeling》2009,15(1):67-77
The tautomerism and intramolecular hydrogen shifts of 5-amino-tetrazole in the gas phase were studied in the present work.
The minimum energy path (MEP) information of 5-amino-tetrazole was obtained at the CCSD(T)/6–311G**//MP2/6–311G** level of
theory. The six possible tautomers of 1H, 4H-5-imino-tetrazole (a), 1H-5-amino-tetrazole (b), 2H-5-amino-tetrazole (c), 1H, 2H-5-imino-tetrazole (d), the mesoionic form (e) and 2H, 4H-5-imino-tetrazole (f) were investigated. Among these tautomers, there are 2 amino- forms, 3 imino- forms, and 1 mesoionic structure form. In all
the tautomers, 2-H form (c) is the energetically preferred one in the gas phase. In the imino- tautomers, the energy value of the compound d is similar as that of the compound f but it is higher than the energy value of the compound a. The potential energetic surface (PES) and kinetics for five reactions have been investigated. Reaction 2 (b→c) was hydrogen shifts only in which the 1-H and 2-H rearrangement. This means that the reaction 2 (b→c) is energetically favorable having an activation barrier of 45.66 kcal·mol−1 and the reaction energies (ΔE) is only 2.67 kcal·mol−1. However, the reaction energy barrier for tautomerism of reaction 1 (b→e) is 54.90 kcal·mol−1. Reaction 1 (b→a), reaction 3 (c→d), and reaction 5 (c→f) were amino- →imino- tautomerism reactions. The energy barriers of amino- →imino- tautomerism reactions required are 59.39,
65.57, 73.61 kcal·mol−1 respectively in the gas phase. The calculated values of rate constants using TST, TST/Eckart, CVT, CVT/SCT and CVT/ZCT methods
using the optimized geometries obtained at the MP2/6–311G** level of theory show the variational effects are small over the
whole temperature range, while tunneling effects are big in the lower temperature range for all tautomerism reactions.
Graphical Abstract Figure (DOC 45.0 KB) 相似文献
10.
K. Yamamura 《Population Ecology》2000,42(2):161-169
Two equations have been used frequently to describe the relation between the sample variance (s
2) and sample mean (m) of the number of individuals per quadrat: Taylor's power law, s
2 = am
b
, and Iwao's m
*−m regression, s
2 = cm + dm
2, where a, b, c, and d are constants. We can obtain biological information such as colony size and the degree of aggregation of colonies from parameters
c and d of Iwao's m
*−m regression. However, we cannot obtain such biological information from parameters a and b of Taylor's power law because these parameters have not been described by simple functions. To mitigate such in-convenience,
I propose a mechanistic model that produces Taylor's power law; this model is called the colony expansion model. This model
has the following two assumptions: (1) a population consists of a fixed number of colonies that lie across several quadrats,
and (2) the number of individuals per unit occupied area of colony becomes v times larger in an allometric manner when the occupied area of colony becomes h times larger (v≥ 1, h≥ 1). The parameter h indicates the dispersal rate of organisms. We then obtain Taylor's power law with b = {ln[E(h)] + ln[E(v
2)]}/{ln[E(h)] + ln[E(v)]}, where E indicates the expectation. We can use the inverse of the exponent, 1/b, as an index of dispersal of individuals because it increases with increasing E(h). This model also yields a relation, known as the Kono–Sugino relation, between the proportion of occupied quadrats and the
mean density per quadrat: −ln(1 −p) = fm
g
, where p is the proportion of occupied quadrats, f is a constant, and g = ln[E(h)]/{ln[E(h)] + ln[E(v)]}. We can use g as an index of dispersal as it increases with increasing E(h). The problem at low densities where Taylor's power law is not applicable is also discussed.
Received: January 27, 2000 / Accepted: June 20, 2000 相似文献
11.
Photosynthetic Response of Carrots to Varying Irradiances 总被引:7,自引:3,他引:4
Response to irradiance of leaf net photosynthetic rates (P
N) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled
environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m−2 s−1 at 20 °C and 350 μmol (CO2) mol−1(air). The values of P
N were fitted to a rectangular hyperbolic nonlinear regression model. P
N for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher P
N than CC. None of the cultivars reached saturation at 1 000 μmol m−2 s−1. The predicted P
N at saturation (P
Nmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO2) m−2 s−1, respectively. The compensation irradiance (I
c) occurred at 54 μmol m−2 s−1 for Cascade, 36 μmol m−2 s−1 for CC, 45 μmol m−2 s−1 for Oranza, and 25 μmol m−2 s−1 for RCC. The quantum yield among the cultivars ranged between 0.057–0.033 mol(CO2) mol−1(PAR) and did not differ. Dark respiration varied from 2.66 μmol m−2 s−1 for Cascade to 0.85 μmol m−2 s−1 for RCC. As P
N increased with PAR, intercellular CO2 decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between
600 and 800 μmol m−2 s−1 followed by a steep decline resulting in sharp increases in water use efficiency.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
Photosynthetic parameters, growth, and pigment contents were determined during expansion of the fourth leaf of in vitro photoautotrophically cultured Nicotiana tabacum L. plants at three irradiances [photosynthetically active radiation (400–700 nm): low, LI 60 μmol m−2 s−1; middle, MI 180 μmol m−2 s−1; and high, HI 270 μmol m−2 s−1]. During leaf expansion, several symptoms usually accompanying leaf senescence appeared very early in HI and then in MI plants.
Symptoms of senescence in developing leaves were: decreasing chlorophyll (Chl) a+b content and Chl a/b ratio, decreasing both maximum (FV/FM) and actual (ΦPS2) photochemical efficiency of photosystem 2, and increasing non-photochemical quenching. Nevertheless, net photosynthetic
oxygen evolution rate (P
N) did not decrease consistently with decrease in Chl content, but exhibited a typical ontogenetic course with gradual increase.
P
N reached its maximum before full leaf expansion and then tended to decline. Thus excess irradiance during in vitro cultivation did not cause early start of leaf senescence, but impaired photosynthetic performance and Chl content in leaves
and changed their typical ontogenetic course. 相似文献
13.
This article reports rate constants for thiol–thioester exchange (k
ex), and for acid-mediated (k
a), base-mediated (k
b), and pH-independent (k
w) hydrolysis of S-methyl thioacetate and S-phenyl 5-dimethylamino-5-oxo-thiopentanoate—model alkyl and aryl thioalkanoates, respectively—in water. Reactions such as
thiol–thioester exchange or aminolysis could have generated molecular complexity on early Earth, but for thioesters to have
played important roles in the origin of life, constructive reactions would have needed to compete effectively with hydrolysis
under prebiotic conditions. Knowledge of the kinetics of competition between exchange and hydrolysis is also useful in the
optimization of systems where exchange is used in applications such as self-assembly or reversible binding. For the alkyl
thioester S-methyl thioacetate, which has been synthesized in simulated prebiotic hydrothermal vents, k
a = 1.5 × 10−5 M−1 s−1, k
b = 1.6 × 10−1 M−1 s−1, and k
w = 3.6 × 10−8 s−1. At pH 7 and 23°C, the half-life for hydrolysis is 155 days. The second-order rate constant for thiol–thioester exchange
between S-methyl thioacetate and 2-sulfonatoethanethiolate is k
ex = 1.7 M−1 s−1. At pH 7 and 23°C, with [R″S(H)] = 1 mM, the half-life of the exchange reaction is 38 h. These results confirm that conditions
(pH, temperature, pK
a of the thiol) exist where prebiotically relevant thioesters can survive hydrolysis in water for long periods of time and
rates of thiol–thioester exchange exceed those of hydrolysis by several orders of magnitude. 相似文献
14.
The copper(II), nickel(II) and silver(I) complexes of the pentadentate 17-membered macrocycle 1, 12, 15-triaza-3, 4:9, 10-dibenzo-5,8-dithiacycloheptadecane (L1) have been prepared as perchlorates and characterized by X-ray crystallography. The N3S2 ligand uses all donor atoms for complexation. The copper coordination is square pyramidal with one sulfur atom in the axial site. Ni(II) displays an octahedral coordination by an interaction with a water molecule. The Ag(I) coordination is best described as a distorted pentagonal bipyramid. In [CuL1]2+ the 1, 4, 7-triazaheptane fragment of L1 is meridionally coordinated, but facially in [NiL1(H2O)]2+ and intermediate in [AgL1](ClO4). Crystal data for [CuL1](ClO4)2: monoclinic, space group P21/n, a = 13.153(8), b = 11.951(5), c = 17.880(8)Å, β = 110.29(4)°, Z = 4, R = 0.086 for 2732 independent reflections with I 2σ(I); [NiL1(H2O)](ClO4)2: monoclinic, P21/a, a = 10.771(2), b= 16.157(2), c = 15.286(2) Å, β =93.08(1)°, Z = 4, R = 0.085 for 1464 independent reflections with I 2σ(I); [AgL1](ClO4): monoclinic, P21/n, a = 12.708(9), b = 9.483(7), c = 19.569(13) Å, β= 103.95(6)°, Z = 4, R = 0.039 for 3600 independent reflections with I 2σ(I). 相似文献
15.
Near-isogenic lines of maize varying in their genes for flavonoid biosynthesis were utilized to examine the effects of foliar
flavonoids and nutrient deficiency on maximum net photosynthetic rate (P
N) and chlorophyll (Chl) fluorescence (Fv/Fm) in response to ultraviolet-B (UV-B) radiation. Plants with deficient (30 to 70 % lower N, K, Mn, Fe, and Zn) and sufficient
nutrients were exposed to four irradiation regimes: (1) no UV-B with solar photosynthetically active radiation (PAR), (2) two day shift to ambient artificial UV-B, 8.2–9.5 kJ m−2 d−1 (21–25 mmol m−2 d−1); (3) continuous ambient artificial UV-B; (4) continuous solar UV-B in Hawaii 12–18 kJ m−2 d−1 (32–47 mmol m−2 d−1). The natural ratio of UVB: PAR (0.25–0.40) was maintained in the UV-B treatments. In the adequately fertilized plants, lines
b and lc had higher contents of flavonoids and anthocyanins than did lines hi27 and dta. UV-B induced the accumulation of
foliar flavonoids in lines hi27 and b, but not in the low flavonoid line dta or in the high flavonoid line lc. In plants grown
on deficient relative to adequate nutrients, flavonoid and anthocyanin contents decreased by 30–40 and 40–50 %, respectively,
and Chl a and Chl b contents decreased by 30 and 70 %, respectively. The UV-B treatments did not significantly affect P
N and Fv/Fm in plants grown on sufficient nutrients, except in the low flavonoid lines dta and hi27 in which P
N and Fv/Fm decreased by ∼15 %. P
N, Fv/Fm, and stomatal conductance decreased markedly (20–30 %) in all lines exposed to UV-B when grown on low nutrients. The decrease
in Fv/Fm was 10 % less in higher flavonoid lines b and lc. The photosynthetic apparatus of maize readily tolerated ambient UV-B in
the tropics when plants were adequately fertilized. In contrast, ambient UV-B combined with nutrient deficiency significantly
reduced photosynthesis in this C4 plant. Nutrient deficiency increased the susceptibility of maize to UV-B-induced photoinhibition in part by decreasing the
contents of photoprotective compounds. 相似文献
16.
Myron A. Peck Lawrence J. Buckley David A. Bengtson 《Environmental Biology of Fishes》2006,75(4):419-429
Synopsis The routine swimming speed (S) of three groups of 4, 9 and 32 cm total length (LT) juvenile cod (Gadus morhua) was quantified in the laboratory at 6 – 10 different temperatures (T) between 3.2 and 16.7°C. At temperatures between 5 and 15°C, mean group S increased exponentially with increasing T (S=a ebT) and the effect of temperature (b = 0.082, Q10 = 2.27) was not significantly different among the groups (over the 8-fold difference in fish sizes of early- and post-settlement
juveniles). Differences in mean S among individuals within each group were quite large (coefficient of variation = 40 – 80%). Swimming data for juveniles and
those collected for groups of 0.4, 0.7 and 0.9 cm standard length (LS) larvae were combined to assess the effect of body size on S. At 8°C, S (mm s−1) increased with LS (mm) according to: S = 0.26LSΦ−5.28LS−1, where Φ = 1.55LS−0.08. Relative S (body lengths s−1) was related to LS by a dome-shaped relationship having a maximum value (0.49 body lengths s−1) at 18.5 – 19 mm LS corresponding to the sizes of fish at the end of larval-juvenile metamorphosis. Previous larval cod IBM’s using a cruise-predator
mode likely overestimated rates of foraging (prey searching and encounters) by a factor of ~2, whereas foraging rates in pause-travel
models are closer to estimates of swimming velocities obtained in this and other laboratory studies. 相似文献
17.
Deyong Sun Yunmei Li Qiao Wang Heng Lv Chengfeng Le Changchun Huang Shaoqi Gong 《Hydrobiologia》2010,644(1):337-349
Light scattering, backscattering, and absorption coefficients of particles were observed at 62 locations in Lake Taihu (China)
in November 2008. A method using a priori knowledge and the measured data was proposed to partition particulate scattering
and absorption into contributions of phytoplankton and non-algal particles. The results showed that phytoplankton weakly contributed
to the particulate scattering and backscattering with the mean b
ph/b
p values usually below 10% and b
bph/b
bt values of 0.3–3.9% in the whole visible light spectrum, and an approximate relationship of b
bt ≈ b
bp ≈ b
bnap was regarded as reasonable in Lake Taihu. In contrast with scattering and backscattering, phytoplankton made more contributions
to the particulate absorption with the mean a
ph/a
p values varying in a wide range of about 20–70%. Both the scattering and absorption spectra of non-algal particles can be
modeled well by corresponding methods. A power function model was used to simulate the scattering spectra, which presented
high predictive accuracies with MAPE values usually below 5% and RMSE values below 1.5 m−1, while the spectral absorption model also performed well with mean S
nap being 0.0052 nm−1 (standard deviation, SD = 0.0010 nm−1). As to the phytoplankton absorption, a quadratic function model used was considered to have a good performance with corresponding
parameters being supported at each wavelength in the spectral range of 400–700 nm. Additionally, two basic bio-optical parameters
were determined, that is, b
nap*(550) = 0.604 m2 g−1 and a
ph*(675) = 0.0288 m2 mg−1. Overall, these results obtained in the present study supply us with new knowledge about optical properties of suspended
particulates in an inland and highly turbid lake (Lake Taihu), which are beneficial to the development of analytical models
of water color remote sensing. 相似文献
18.
Summary Cells ofCandida shehatae repressed by growth in glucose- or D-xylose-medium produced a facilitated diffusion system that transported glucose (K
s±2 mM,V
max±2.3 mmoles g−1 h−1),d-xylose (K
s±125 mM,V
max±22.5 mmoles g−1 h−1) and D-mannose, but neither D-galactose norl-arabinose.
Cells derepressed by starvation formed several sugar-proton symports. One proton symport accumulated 3-0-methylglucose about
400-fold and transported glucose (K
s±0.12 mM,V
max ± 3.2 mmoles g−1 h−1) andd-mannose, a second proton symport transportedd-xylose (K
s± 1.0 mM,V
max 1.4 mmoles g−1 h−1) andd-galactose, whilel-arabinose apparently used a third proton symport. The stoicheiometry was one proton for each molecule of glucose or D-xylose
transported. Substrates of one sugar proton symport inhibited non-competitively the transport of substrates of the other symports.
Starvation, while inducing the sugar-proton symports, silenced the facilitated diffusion system with respect to glucose transport
but not with respect to the transport of D-xylose, facilitated diffusion functioning simultaneously with thed-xylose-proton symport. 相似文献
19.
Hoh JF Withers KW Zhong WW 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2008,178(3):279-284
The effect of drug-induced hypothyroidism on ventricular myosin gene expression was explored in a small marsupial, Antechinus flavipes. Pyrophosphate gel electrophoresis, SDS-PAGE and western blotting were used to analyse changes in native myosin isoforms
and myosin heavy chains (MyHCs) in response to hypothyroidism. In some animals, five instead of the normal three native myosin
components were found: V1a, V1b,V1c, V2 and V3, in order of decreasing mobility. In western blots, V1a, V1b, and V1c reacted with anti-α-MyHC antibody, but not with anti-β-MyHC, whereas V2 and V3 reacted with anti-β-MyHC antibody. SDS-PAGE of the unusual ventricular myosins revealed three MyHC isoforms, two of which
bound anti-α-MyHC antibody while the third bound anti-β-MyHC antibody. We conclude that V1a, V1b, V1c are triplets arising from the dimerization of two distinct α-MyHC isoforms. Hypothyroidism, verified by metabolic studies,
decreased α-MyHC content significantly (t-test, P < 0.001) from 91.6 ± 5.9% (SEM, n = 4) in control animals to 67.2 ± 5.7% (SEM, n = 4) in hypothyroid animals, with a concomitant increase in β-MyHC content. We conclude that in adult marsupials, ventricular
myosins are also responsive to changes in the thyroid state as found in eutherians, and suggest that evolution of the molecular
mechanisms underlying this thyroid responsiveness predate the divergence of marsupials and eutherians. 相似文献
20.
Guido Ferretti Massimo Girardis Christian Moia Guglielmo Antonutto 《European journal of applied physiology and occupational physiology》1998,78(5):398-402
The hypothesis was tested that prolonged bed rest impairs O2 transport during exercise, which implies a lowering of cardiac output Q˙
c and O2 delivery (aO2). The following parameters were determined in five males at rest and at the steady-state of the 100-W exercise before (B)
and after (A) 42-day bed rest with head-down tilt at −6°: O2 consumption (V˙O2), by a standard open-circuit method; Q˙
c, by the pressure pulse contour method, heart rate ( f
c), stroke volume (Q
h), arterial O2 saturation, blood haemoglobin concentration ([Hb]), arterial O2 concentration (C
aO2), and Q˙
aO2. The V˙O2 was the same in A and in B, as was the resting f
c. The f
c at 100 W was higher in A than in B (+17.5%). The Q
h was markedly reduced (−27.7% and −22.2% at rest and 100 W, respectively). The Q˙
c was lower in A than in B [−27.6% and −7.8% (NS) at rest and 100 W, respectively]. The C
aO2 was lower in A than in B because of the reduction in [Hb]. Thus also Q˙
aO2 was lower in A than in B (−32.0% and −11.9% at rest and at 100 W, respectively). The present results would suggest a down-regulation
of the O2 transport system after bed rest.
Accepted: 22 April 1998 相似文献