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1.
This paper develops an impulsive SUI model of human immunodeficiency virus/acquired immunodeficiency syndrome(HIV/AIDS) epidemic for the first time to study the dynamic behavior of this model. The SUI model is described by impulsive partial differential equations. First, the well-posedness of the model is attained by the method of characteristic lines and iterative method. Secondly, the basic reproduction number R0(q,T) of the epidemic which depends on the impulsive HIV-finding period T and the HIV-finding proportion q is obtained by mathematical analysis. Our result shows that HIV/AIDS epidemic can be theoretically eradicated if we can have the suitable HIV-finding proportion q and the impulsive HIV-finding period T such that R0(q,T)<1. We also conjecture that the infection-free periodic solution of the SUI model is unstable when R0(q,T)>1.  相似文献   

2.
3.
The influence on the melting of calf thymus and plasmid DNA of cationic lipids of the type used in gene therapy was studied by ultraviolet spectrophotometry and differential scanning calorimetry. It was found that various membrane-forming cationic lipids are able to protect calf thymus DNA against denaturation at 100°C. After interaction with cationic lipids, the differential scanning calorimetry melting profile of both calf thymus and plasmid DNA revealed two major components, one corresponding to a thermolabile complex with transition temperature, Tm(labile), close to that of free DNA and a second corresponding to a thermostable complex with a transition temperature, Tm(stable), at 105 to 115°C. The parameter Tm(stable) did not depend on the charge ratio, R(±). Instead, the amount of thermostable DNA and the enthalpy ratio ΔH(stable)H(labile) depended upon R(±) and conditions of complex formation. In the case of O-ethyldioleoylphosphatidylcholine, the cationic lipid that was the main subject of the investigation, the maximal stabilization of DNA exceeded 90% between R(±) = 1.5 and 3.0. Several other lipids gave at least 75% protection in the range R(±) = 1.5 to 2.0. Centrifugal separation of the thermostable and thermolabile fractions revealed that almost all the transfection activity was present at the thermostable fraction. Electron microscopy of the thermostable complex demonstrated the presence of multilamellar membranes with a periodicity 6.0 to 6.5 nm. This periodic multilamellar structure was retained at temperatures as high as 130°C. It is concluded that constraint of the DNA molecules between oppositely charged membrane surfaces in the multilamellar complex is responsible for DNA stabilization.  相似文献   

4.
If a non-indigenous species is to thrive and become invasive it must first persist under its new set of environmental conditions. Net reproductive rate (R 0) represents the average number of female offspring produced by a female over its lifetime, and has been used as a metric of population persistence. We modeled R 0 as a function of ambient water temperature (T) for the invasive marine calanoid copepod Pseudodiaptomus marinus, which is introduced to west coast of North America from East Asia by ship ballast water. The model was based on temperature-dependent stage-structured population dynamics given by a system of ordinary differential equations. We proposed a methodology to identify habitats that are non-invasible for P. marinus using the threshold of R 0(T) < 1 in order to identify potentially invasible habitats. We parameterized the model using published data on P. marinus and applied R 0(T) to identify the range of non-invasible habitats in a global scale based on sea surface temperature data. The model predictions matched the field evidence of species occurrences well.  相似文献   

5.
In view of the wide applicability and versatility of titanium based Lewis acids in selective organic synthesis including asymmetric synthesis, we have synthesized a family of mono and polyatomic titanium derivatives. The polymetallic complexes prepared are bridged by pyridimine, quinone and triazine based ligands. The synthesis of [{Ti(O-i-Pr)3(Oddbf)}2] (1), [Ti(O-i-Pr)2(Oddbf)2] (2), [{Ti(O-i-Pr)2(Oddbf)(OMent)}2] (3) (ddbfO = 2,3-dihydro-2,2-dimethyl-benzofuranoxo; MentO = (1R,2S,5R)-(−)-menthoxo), [{Ti(O-i-Pr)3(OMenpy)}2] (4), [Ti(O-i-Pr)2(OMenpy)2] (5) (MenpyO = (1S,2S,5R)-(−)-menthoxo-pyridine); [{(Ti(OR)3)2L}n] (RO = isopropoxo, (1R,2S,5R)-(−)-menthoxo) (6-11) and [{(Ti(O-i-Pr)3)3L}n] (12) was accomplished from a Lewis acid such as Ti(O-i-Pr)4, [{Ti(O-i-Pr)3(OMent)}2] or [Ti(OMent)4] and chelating ligands (ddbfOH = 2,3-dihydro-2,2-dimethyl-benzofuranol; MenpyOH = (1R,2S,5R)-(−)-5-methyl-2-isopropyl-1-(2′-pyridinyl)cyclohexan-1-ol; LH2 = 4,6-dihydroxy-2,5-diphenyl-pyrimidine, 2,4-dihydroxy-5,6-dimethyl-pyrimidine, 5,8-dihydroxy-1,4-napthoquinone, 2,5-dihydroxy-1,4-benzoquinone and LH3 = cyanuric acid) that provide a rigid framework for the metal centre. The molecular structure of 5 has been determined by single crystal X-ray diffraction studies.  相似文献   

6.
Cross-Correlation Functions for a Neuronal Model   总被引:5,自引:1,他引:4       下载免费PDF全文
Cross-correlation functions, RXY(t,τ), are obtained for a neuron model which is characterized by constant threshold θ, by resetting to resting level after an output, and by membrane potential U(t) which results from linear summation of excitatory postsynaptic potentials h(t). The results show that: (1) Near time lag τ = 0, RXY(t,τ) = fU [θ-h(τ), t + τ] {h′(τ) + EU [u′(t + τ)]} for positive values of this quantity, where fU(u,t) is the probability density function of U(t) and EU [u′(t + τ)] is the mean value function of U′(t + τ). (2) Minima may appear in RXY(t,τ) for a neuron subjected only to excitation. (3) For large τ, RXY(t,τ) is given approximately by the convolution of the input autocorrelation function with the functional of point (1). (4) RXY(t,τ) is a biased estimator of the shape of h(t), generally over-estimating both its time to peak and its rise time.  相似文献   

7.
A rare subset of HIV-infected individuals, designated viremic non-progressors (VNP), remain asymptomatic and maintain normal levels of CD4+ T-cells despite persistently high viremia. To identify mechanisms potentially responsible for the VNP phenotype, we compared VNPs (average >9 years of HIV infection) to HIV-infected individuals who have similar CD4+ T-cell counts and viral load, but who are likely to progress if left untreated (“putative progressors”, PP), thus avoiding the confounding effect of differences related to substantial CD4+ T cell depletion. We found that VNPs, compared to PPs, had preserved levels of CD4+ stem cell memory cells (TSCM (p<0.0001), which was associated with decreased HIV infection of these cells in VNPs (r = −0.649, p = 0.019). In addition, VNPs had decreased HIV infection in CD4+ central memory (TCM) cells (p = 0.035), and the total number of TCM cells was associated with increased proliferation of memory CD4+ T cells (r = 0.733, p = 0.01). Our results suggest that, in HIV-infected VNPs, decreased infection of CD4+ TCM and TSCM, cells are involved in preservation of CD4+ T cell homeostasis and lack of disease progression despite high viremia.  相似文献   

8.
Cell cycle is controlled at two restriction points, R 1 and R 2. At both points the cell will commit apoptosis if it detects irreparable damage. But at R 1 an undamaged cell also decides whether to proceed to the S phase or go into a quiescent mode, depending on the environmental conditions (e.g., overpopulation, hypoxia). We consider the effect of this decision at the population level in a spherical tissue {r < R(t)}. We prove that if the cells have full control at R 1, they can manipulate the size of R(t) to ensure that 0 < cR(t) ≤ C < ∞; simulations further show that R(t) can be made nearly stationary. In the absence of such control, R(t) will either increase to ∞ or decrease to 0. The mathematical model and analysis involve a system of PDEs in {r < R(t)}.  相似文献   

9.
10.
The combined thermal load created by exercise and a hot environment is associated with an exaggerated core temperature response. The elevated core temperature is believed to increase the total stress of the exercise. Increased stress during exercise has been associated with increased levels of cortisol. The association of cortisol with increased inflammatory responses following exercise in the heat is equivocal. Thus, the purpose of the current investigation was to explore the relationship between increases in rectal temperature (Tre) and TNFα and cortisol. To induce Tre changes, 8 male subjects (mean±SD, age=23.6±2 yr, VO2max=52.8±3.7 mL/kg/min, BMI=24.2±1.9) participated in two 40 min trials of cycle ergometry at 65% of VO2peak immersed to chest level in cool (25 °C) and warm (38.5 °C) water. Tre was monitored throughout each trial, with blood samples taken immediately pre and post of each trial. Neither cortisol nor TNFα changed significantly during exercise in the cool water; however, in the warm trial, both cortisol and TNFα significantly increased (p<0.004). Concordance correlations (Rc) between Δ cortisol and Δ TNFα indicated a strong but non-significant correlation (Rc=0.833, p=0.135). In conclusion, changes in core temperature may be impacting the relationship between exercise induced changes in cortisol and TNFα. Therefore, acute moderate-intensity exercise (40 min or less) in warm water impacts the stress and inflammatory response. Understanding this is important because exercise load may need to be adjusted in warm and hot environments to avoid the negative effects of elevated stress and inflammation response.  相似文献   

11.
The [PdII{(R,R)-chxn}(OH)2] reagent (chxn = 1,2-diaminocyclohexane) is introduced as a metal probe for the detection of the bidentate chelating sites of a glycose. Two moles of hydroxide per mole palladium support double deprotonation of potentially chelating diol functions at a glycose’s backbone. The individual chelating sites are detected using one- and two-dimensional NMR techniques. At equimolar amounts of palladium(II) and aldose, the metal-binding sites include mostly the hydroxy function at the anomeric carbon atom. Chelators are derived from both the pyranose and the furanose isomers. Most pyranose-based chelators form five-membered chelate rings by using their 1,2-diol function. Though 1,2-diolate bonding is also common to the furanoses, the formation of six-membered chelate rings by 1,3-bonding is more significant for them. Metal-excess conditions provoke mostly bis-bidentate 1,2;3,4-chelation but unusual isomers form also: thus d-xylose is dimetallated in its all-axial β-pyranose form, and erythrose’s dimetallation results in the formation of two isomers of a metal derivative of the open-chain hydrate. The spectroscopic results are supported by crystal-structure determinations on [Pd{(R,R)-chxn}(α-d-Xylp1,2H−2O1,2)]·H2O (Xyl = xylose), [Pd{(R,R)-chxn}(α-d-Ribp1,2H−2O1,2)]·2.25H2O (Rib = ribose), [Pd{(R,R)-chxn}(α-l-Thrf1,3H−2O1,3)]·2H2O (Thr = threose) and [Pd{(R,R)-chxn}(α-d-Eryf1,3H−2O1,3)]·3H2O (Ery = erythrose).  相似文献   

12.
(1)
Rectal temperature (Tr) was measured in captive African giant rats (Cricetomys gambianus, Waterhouse), live-trapped in the Savannah during the harmattan, hot-dry and rainy seasons with the aim of determining diurnal, seasonal and sex patterns.
(2)
Mean (±SEM) Tr in the morning (37.16±0.04 °C) was lower (P<0.001) than the afternoon (37.49±0.03 °C) and evening (37.66±0.03 °C). There was no significant difference (P>0.05) between afternoon and evening Tr during the harmattan and rainy seasons, but the difference was significant (P<0.001) during the hot-dry season. Overall Tr was higher (P<0.001) during the hot-dry (38.03±0.03 °C) than harmattan (37.17±0.03 °C) and rainy (37.21±0.03 °C) seasons. Tr of bucks was lower than that of does (P<0.0001) during the harmattan and rainy seasons, but sex difference during the hot-dry season was not significant (P>0.05).
(3)
Base-line Tr values for the African giant rats are shown for the first time. Season, time of day and sex influence fluctuations in Trs of African giant rats, and should be considered during diagnostic and clinical evaluations.
  相似文献   

13.
Bis(azido)bis(phosphine)-Pd(II) and -Pt(II) complexes, [M(N3)2L2] {L = PMe3, PEt3, PMe2Ph, dppe = 1,2-bis(diphenylphosphino)ethane}, underwent 1,3-dipolar cycloaddition with organic chiral isothiocyanates (R-NCS: R = (S)-(+)-1-phenylethyl, (R)-(−)-1-phenylethyl, (±)-1-phenylethyl, (S)-(+)-1-indanyl) to give the corresponding tetrazole-thiolato Pd(II) and Pt(II) complexes, trans-[M{S[CN4(R)]}2L2] or [M{S[CN4(R)]}2(dppe)]. Spectroscopic (IR and NMR) and X-ray structural analyses of the products showed that the absolute configuration of the starting organic isothiocyanates is retained throughout the reaction. Further treatments of the isolated tetrazole-thiolato complexes with electrophiles such as HCl or benzoyl chloride produced heterocyclic compounds containing a tetrazole thione or a tetrazolyl sulfide group. In addition, organic tetrazole thiones, [S = {CN4H(R)}] containing a chiral moiety, were prepared from NaN3 and R-NCS in the presence of water.  相似文献   

14.
Substituted salicylaldehydes [C6HR1R2R3(CHO)(OH)] react with CoMe3(PMe3)3 to afford 6-coordinate (cis-dimethyl)(2-formyl-phenolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[C6HR1R2R3(CHO)(O)Me2](PMe3)2 (1: R1 = H; R2 = Me; R3 = tert-Bu; 2: R1, R2 = C6H4; R3 = H). Accordingly, substituted enolated malonic dialdehydes (CHO-CR4CR5-OH) react with CoMe3(PMe3)3 to afford 6-coordinate (cis-dimethyl)(2-formyl-enolato)trans-bis(trimethylphosphine)cobalt(III) compounds Co[(CHO-CR4CR5-O)(Me)2](PMe3)2 (3: R4, R5 = (CH2)2C6H4; 4: R4 = R5 = C6H5). In the molecular structure of 4, the cobalt atom is centred in an octahedral coordination geometry brought about by a six-membered chelate ring (O:O-ligand), cis-dimethyl and trans-trimethylphosphine groups. A reaction mechanism is suggested.  相似文献   

15.
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   

16.
A chiral spin crossover iron(II) complex, fac-Λ-[FeII(HLR)3](ClO4)2·EtOH was synthesized and its crystal structures in both the high-spin (HS) and low-spin (LS) states were determined, where HLR denotes 2-methylimidazol-4-yl-methylideneamino-R-(+)-1-methylphenyl. The complex assumes octahedral coordination geometry of N6 donor atoms by three bidentate ligands HLR. The complex exists as the facial-Λ-isomer of fac-Λ-[FeII(HLR)3]2+ of the possible geometrical fac- and mer-isomers and the Δ- and Λ-enantiomorphs. The X-ray structural analyses revealed that the R-form of the ligand (HLR) induces the fac-Λ-isomer of fac-Λ-[FeII(HLR)3]2+ and the S-form of the ligand (HLS) induces the fac-Δ-isomer of fac-Δ-[Fe(HLS)3]2+. The complex fac-Λ-[FeII(HLR)3](ClO4)2·EtOH shows a complete steep spin crossover between the HS and the LS states at T1/2 = 195 K.  相似文献   

17.
Reactions of 2-(arylazo)aniline, HL [H represents the dissociable protons upon orthometallation and HL is p-RC6H4N = NC6H4-NH2; R = H for HL1; CH3 for HL2 and Cl for HL3] with Ru(R1-tpy)Cl3 (where R1-tpy is 4′-(R1)-2,2′,6′′,2′′-terpyridine and R1 = H or 4-N,N-dimethylaminophenyl or 4-methylphenyl) afford a group of complexes of type [Ru(L)(R1-tpy)]·ClO4 each of which contains C,N,N coordinated L as a tridentate ligand along with a terpyridine. Structure of one such complex has been determined by X-ray crystallography. All the Ru(II) complexes are diamagnetic, display characteristic 1H NMR signals and intense dπ(RuII) → π∗(tpy) MLCT transitions in the visible region. Cyclic voltammetric studies on [Ru(L)(R1-tpy)]·ClO4 complexes show Ru(II)-Ru(III) oxidation within 0.63-0.67 V versus SCE.  相似文献   

18.
The purpose of this study was to investigate ethnic differences in cutaneous thermal sensation thresholds and the inter-threshold sensory zone between tropical (Malaysians) and temperate natives (Japanese). The results showed that (1) Malaysian males perceived warmth on the forehead at a higher skin temperature (Tsk) than Japanese males (p<0.05), whereas cool sensations on the hand and foot were perceived at a lower Tsk in Malaysians (p<0.05); (2) Overall, the sensitivity to detect warmth was greater in Japanese than in Malaysian males; (3) The most thermally sensitive body region of Japanese was the forehead for both warming and cooling, while the regional thermal sensitivity of Malaysians had a smaller differential than that of Japanese; (4) The ethnic difference in the inter-threshold sensory zone was particularly noticeable on the forehead (1.9±1.2 C for Japanese, 3.2±1.6 °C for Malaysians, p<0.05). In conclusion, tropical natives had a tendency to perceive warmth at a higher Tsk and slower at an identical speed of warming, and had a wider range of the inter-threshold sensory zone than temperate natives.  相似文献   

19.
The degree of polarization of fluorescence from stretched Chironomus thummi polytene chromosomes, stained with low concentrations of acridine orange (AO), decreases with increasing temperature. The "half temperature" of this decrease (T½R) is lower than the expected DNA thermal denaturation temperature (Tm) by about 20°C. T½R is lowered as histone is removed from chromosomes. Balbiani ring regions of the fourth chromosome have T½R's much lower than other regions, and nearly as low as chromosomes which had been extensively pretreated with trypsin to remove histone and other proteins. Measurements of the thermal change in the rotational diffusion rate of AO in solution with DNA indicate that the temperature at which the DNA-AO bonding changes from a "rigid" to a "loose" mode varies with the GC percentage of the DNA, and in the same fashion as Tm, although 20°C lower.  相似文献   

20.
The new chiral and functionalized cyclic binaphthoxyphosphazenes R,R,R-[N3P3(O2C20H10Br2)3] (R-1), R,R,R-[N3P3(O2C20H10(CCSiMe3)2)3] (R-2), and the high molecular weight linear polymers R/S-[NP(O2C20H10Br2)]n (R/S-3), R-[NP(O2C20H10Br2)]n (R-3), and R-{NP[O2C20H10(CCSiMe3)2]}n, (R-4), with Mw on the order of 106 and very high Tg, have been synthesized and characterized by IR and NMR spectroscopy. The optically active polymer (R-3) was configurationally stable below 300 °C, but at higher temperatures an atropisomerization process took place that became faster near the glass transition temperature (ca. 350 °C).  相似文献   

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