Large R0 Research Articles

Realization of double uniform line self-focusing of elliptical Airyprime beams

Double line self-focusing characteristics of elliptical Airyprime beams (EAPBs) with different elliptical vertical-axis factor β are investigated by varying the main ring radius r0. Overly large or small r0 results in the inhomogeneous distribution of light intensity at one linear focus of the double line self-focusing. Only when r0 is appropriate and β is within a certain range, can double uniform line self-focusing happen to the EAPB. Moreover, the self-focusing ability of the second line self-focusing is weaken than that of the first line self-focusing. Under the premise of our selected values of beam parameters, the EAPB can achieve double uniform line self-focusing when r0 = 0.3 mm and β = 0.58∼0.71. The focal length of the first line self-focusing, the lengths of double linear focus, and the self-focusing abilities of the double uniform line self-focusing can be regulated by varying β within the range of 0.58∼0.71. If β is smaller than 0.58 or larger than 0.71, it will lead to nonuniform line self-focusing. An explanation of the physical mechanism behind the double uniform line self-focusing of the EAPB is proposed. Finally, the experimental measurements of the line self-focusing of the EAPB confirm the validity of the above conclusions. This research provides a new solution on how to generate double uniform line self-focusing and new insights into the practical application of elliptical self-focusing beams.

Effects of straw-returning combined with application of microbial inoculants on soil aggregates and related nutrients

We analyzed the particle size distribution of soil aggregates in 0-20 and 20-40 cm soil layers of rice-wheat rotation field based on a field plot test with two treatments, conventional straw returning (CK) and straw returning with the addition of straw decomposition promoting microbial inoculants (IT). We evaluated the water stability indices of soil aggregates (the number of soil water stable large aggregates R0.25, the average weight diameter MWD, and the geometric average diameter GMD), and measured the contents of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) in the soil aggregates of ＜0.053, 0.053-0.25, 0.25-1, ＞1 mm. The results showed that: 1) The number of aggregates ＜0.053, 0.053-0.25, ＞0.25 mm in the 0-20 and 20-40 cm soil layers under IT decreased by 10.0% and 6.8%, increased by 3.0% and 5.7%, and 17.9% and 26.1% compared with CK, respectively. IT effectively increased R0.25, MWD, and GMD by 26.4%, 20.0%, 18.2% and 18.2%, 10.5%, 10.0% in 0-20 and 20-40 cm soil, respectively. 2) Compared to CK, the TP content of 0.25-1 mm aggregates in 0-20 and 20-40 cm soil under IT was significantly increased by 40.3% and 37.5%, respectively, without difference in TN and SOC contents. There was no significant difference in nutrient contents of the other aggregates between the treatments. The contents of SOC and TN in large aggregates (>0.25 mm) were higher than those in silty aggregates (<0.053 mm). Compared to CK, the cumulative contribution rates of SOC, TN and TP of <0.053 mm aggregates under IT were decreased in two soil layers. There was no significant difference in the nutrient cumulative contribution rates of 0.053-0.25 mm aggregates between treatments. The cumulative contribution rates of SOC, TN, and TP of large aggregates (>0.25 mm) under IT were 32.1%, 19.6%, 52.8% and 22.8%, 11.8%, 42.9% higher than those under CK in 0-20 and 20-40 cm soils, respectively. 3) The number of <0.053 mm aggregates was significantly negatively correlated with SOC and TP contents, while that of 0.053-0.25 mm aggregates was negatively correlated with nutrient content. The number of large aggregates (>0.25 mm) were significantly positively correlated with SOC, TN, and TP contents. In conclusion, straw returning with microbial-inoculant addition could promote the formation of soil macroaggregates (>0.25 mm), and improve the water stability of soil aggregates, increasing nutrient contents in soil macroaggregates, with the nutrients transferring from silty aggregates to macroaggregates.

The Dependence of the Location and Pressure Variations of the Martian Magnetic Pileup Boundary on the Interplanetary Magnetic Field: An MHD Simulation Study

Abstract In this paper, using a three-dimensional multispecies MHD model, we study the effect of the interplanetary magnetic field (IMF) intensity and orientation on the subsolar standoff distance of the Martian magnetic pileup boundary (r 0) and the pressure balance across it. The results show that: (1) with the increasing magnitude of the Y- or Z-component of the IMF, B Y or B Z , r 0 increases, while the radial IMF component, B X , has little effect. With the increasing magnitude of B Y or B Z , the compression degree of the magnetic field (f) increases, while the solar wind pressure coefficient (k) remains unchanged, resulting in the enhancement of r 0. (2) Under the same IMF intensity, B t , the impact of the IMF cone angle on r 0 and f is controlled by the ratio of the IMF Y- and Z-components to B t , B Y 2 + B Z 2 / B t . When the ratio is enhanced, both r 0 and f increase, while k generally remains unchanged. Compared with the IMF cone angle, the influence of the IMF clock angle is relatively less. We suggest that the stronger magnetic pileup process controlled by the perpendicular IMFs (B Y or B Z ) causes the larger r 0, while the weaker magnetic pileup under the radial IMF leads to the smaller r 0. The difference in the IMF effect on the size of the Martian magnetic pileup boundary and the terrestrial magnetopause reveals different solar wind interactions with a magnetized and unmagnetized planet. Last, the location of the intense crustal field can also affect r 0 and the pressure balance condition, and the specific impact needs to be further studied.

Life tables of two newly discovered parasitoid wasps, Muscidifura similadanacus and M. sinesensilla (Hymenoptera: Pteromalidae), reared on Musca domestica (Diptera: Muscidae)

ABSTRACT Parasitoids of Muscidifurax spp. are of great value in the biological control of Musca domestica, a harmful pest. In this study, the life tables of two newly discovered parasitoid wasps, M. similadanacus and M. sinesensilla (Hymenoptera: Pteromalidae), were constructed using pupae of M. domestica as the host at 25°C in the laboratory. The parameters of the life tables were calculated and analysed. The differences in lifespan, oviposition period, offspring yield and population growth data between the two species were compared. For the same two species of parasitoids, the net reproductive rate (R0 ) was 123.49 and 38.26, intrinsic rate of increase (rm ) 0.23 and 0.20, finite rate of increase (λ) 1.25 and 1.22, generation time (T) 21.35 and 18.69, and the population doubling time (DT) 3.07 and 3.55, respectively. The results obtained by the jackknife method showed that there were differences in population growth parameters between the two species. M. similadanacus had relatively larger R0 , rm , λ and longer T. Our results suggest that M. similadanacus can be used as a biological control agent for M. domestica, and M. sinesensilla has a potential role in controlling M. domestica.

Global stability in a competitive infection-age structured model

We study a competitive infection-age structured SI model between two diseases. The well-posedness of the system is handled by using integrated semigroups theory, while the existence and the stability of disease-free or endemic equilibria are ensured, depending on the basic reproduction number R0x and R0y of each strain. We then exhibit Lyapunov functionals to analyse the global stability and we prove that the disease-free equilibrium is globally asymptotically stable whenever max{R0x, R0y} ≤ 1. With respect to explicit basin of attraction, the competitive exclusion principle occurs in the case where R0x ≠ R0y and max{R0x, R0y} &gt; 1, meaning that the strain with the largest R0 persists and eliminates the other strain. In the limit case R0x = Ry0 &gt; 1, an infinite number of endemic equilibria exists and constitute a globally attractive set.

R- and K-selection in fluctuating populations is determined by the evolutionary trade-off between two fitness measures: Growth rate and lifetime reproductive success.

In a stable environment, evolution maximizes growth rates in populations that are not density regulated and the carrying capacity in the case of density regulation. In a fluctuating environment, evolution maximizes a function of growth rate, carrying capacity and environmental variance, tending to r-selection and K-selection under large and small environmental noise, respectively. Here we analyze a model in which birth and death rates depend on density through the same function but with independent strength of density dependence. As a special case, both functions may be linear, corresponding to logistic dynamics. It is shown that evolution maximizes a function of the deterministic growth rate r0 and the lifetime reproductive success (LRS) R0 , both defined at small densities, as well as the environmental variance. Under large noise this function is dominated by r0 and average lifetimes are small, whereas R0 dominates and lifetimes are larger under small noise. Thus, K-selection is closely linked to selection for large R0 so that evolution tends to maximize LRS in a stable environment. Consequently, different quantities (r0 and R0 ) tend to be maximized at low and high densities, respectively, favoring density-dependent changes in the optimal life history.

Age-Stage, Two-Sex Life Table Characteristics of Aedes albopictus and Aedes Aegypti in Penang Island, Malaysia.

The life table developmental attributes of laboratory colonies of wild strains of Aedes albopictus and Aedes aegypti were analyzed and compared based on the age-stage, two-sex life table. Findings inclusive in this study are: adult preoviposition periods, total preoviposition period, mean intrinsic rate of increase (r), mean finite rate of increase (λ), net reproductive rates (R0), and mean generation time (T). The total preadult development time was 9.47 days for Ae. albopictus and 8.76 days for Ae. aegypti. The life expectancy was 19.01 days for Ae. albopictus and 19.94 days for Ae. aegypti. Mortality occurred mostly during the adult stage. The mean development time for each stage insignificantly correlated with temperature for Ae. albopictus (r = -0.208, P > 0.05) and (r = -0.312, P > 0.05) for Ae. aegypti. The population parameters suggest that Ae. albopictus and Ae. aegypti populations are r-strategists characterized by a high r, a large R0, and short T. This present study provides the first report to compare the life parameters of Ae. albopictus and Ae. aegypti strains from Penang island, Malaysia.

The basic reproduction number as a predictor for epidemic outbreaks in temporal networks.

The basic reproduction number R 0—the number of individuals directly infected by an infectious person in an otherwise susceptible population—is arguably the most widely used estimator of how severe an epidemic outbreak can be. This severity can be more directly measured as the fraction of people infected once the outbreak is over, Ω. In traditional mathematical epidemiology and common formulations of static network epidemiology, there is a deterministic relationship between R 0 and Ω. However, if one considers disease spreading on a temporal contact network—where one knows when contacts happen, not only between whom—then larger R 0 does not necessarily imply larger Ω. In this paper, we numerically investigate the relationship between R 0 and Ω for a set of empirical temporal networks of human contacts. Among 31 explanatory descriptors of temporal network structure, we identify those that make R 0 an imperfect predictor of Ω. We find that descriptors related to both temporal and topological aspects affect the relationship between R 0 and Ω, but in different ways.

Age problem in Lemaître–Tolman–Bondi void models

As is well known, one can explain the current cosmic acceleration by considering an inhomogeneous and/or anisotropic universe (which violates the cosmological principle), without invoking dark energy or modified gravity. The well-known one of this kind of models is the so-called Lemaître–Tolman–Bondi (LTB) void model, in which the universe is spherically symmetric and radially inhomogeneous, and we are living in a locally underdense void centered nearby our location. In the present work, we test various LTB void models with some old high redshift objects (OHROs). Obviously, the universe cannot be younger than its constituents. We find that an unusually large r0 (characterizing the size of the void) is required to accommodate these OHROs in LTB void models. There is a serious tension between this unusually large r0 and the much smaller r0 inferred from other observations (e.g. SNIa, CMB and so on). However, if we instead consider the lowest limit 1.7 Gyr for the quasar APM 08279+5255 at redshift z=3.91, this tension could be greatly alleviated.

GaN/AlN constant total effective radius multi-wells quantum rings: Physical properties under well number variation effects

In this study, effect of the number of wells and quantum ring thickness on subband electronic structure, ground state wave function, Fermi energy and linear refractive index changes of an AlN/GaN constant total effective radius multi-wells quantum ring have been studied. It is shown that, effect of increasing of the inner quantum ring radius R0 on the ground state energy and other physical properties are larger than increasing of the number of wells. This fact helps the simplification of the experiments, since making quantum ring with larger R0 is easier than making multiple-wells quantum rings. However, effect of the increasing of the R0 values in systems with larger number of wells is also larger. Increase of the R0 also leads to increase of the refractive index changes amplitudes. Resonant energy undergo a red-shift by going from single quantum well system to double quantum well system, and further increasing of the numbers of wells leads to a blue-shift. Finally, we propose number of wells as a tuning tool to select the position of the maximum probability of finding free carriers within the system.

Evolutionary dynamics of infectious diseases in finite populations

In infectious disease epidemiology the basic reproductive ratio, R0, is defined as the average number of new infections caused by a single infected individual in a fully susceptible population. Many models describing competition for hosts between non-interacting pathogen strains in an infinite population lead to the conclusion that selection favors invasion of new strains if and only if they have higher R0 values than the resident. Here we demonstrate that this picture fails in finite populations. Using a simple stochastic SIS model, we show that in general there is no analogous optimization principle. We find that successive invasions may in some cases lead to strains that infect a smaller fraction of the host population, and that mutually invasible pathogen strains exist. In the limit of weak selection we demonstrate that an optimization principle does exist, although it differs from R0 maximization. For strains with very large R0, we derive an expression for this local fitness function and use it to establish a lower bound for the error caused by neglecting stochastic effects. Furthermore, we apply this weak selection limit to investigate the selection dynamics in the presence of a trade-off between the virulence and the transmission rate of a pathogen.

High-Throughput Protein Structural Mapping using Transition Metal FRET

The structures of macromolecules drive their function. Understanding these structures is key to understanding the regulation and activity of biological systems. While X-ray crystallography and NMR are able to provide atomic resolution of many proteins, their usefulness in tracking structures is limited. An alternative method to map dynamic structures is Forster resonance energy transfer (FRET) - a steep distance-dependent process of energy transfer between a donor fluorophore and an acceptor molecule. Classical FRET, however, has been constrained by fluorophore pairs with large R0 values (30 to 60 A) and long chemical linkers. These limitations can be overcome by using small dyes (Fluorescein-5-malemide [F5M] and monobromobimane [mBBr]) as donors and transition metal ions (Ni2+ and Cu2+) as acceptors. Here, we use a high-throughput fluorescent method to rapidly and accurately map short-range distances (5 to 20 A) between residue pairs in the model ligand-binding protein Maltose Binding Protein (MBP). Multiple donor sites were individually labeled with organic dyes while di-histidine metal binding acceptor sites were engineered into α-helices. Distances were measured between donor/acceptor pairs to build a matrix of distances that covers the protein. Combined, these measurements map the three dimensional topology of MBP. By comparing the measured distances from FRET to X-ray crystal structures, we confirm that this method provides accurate backbone distance measurements to within a few angstroms in two independent states of MBP. We conclude that transition metal ion FRET provides rapid angstrom-scale mapping of dynamic protein structures.

Early Outbreak of 2009 Influenza A (H1N1) in Mexico Prior to Identification of pH1N1 Virus

BackgroundIn the aftermath of the global spread of 2009 influenza A (pH1N1) virus, still very little is known of the early stages of the outbreak in Mexico during the early months of the year, before the virus was identified.Methodology/Main FindingsWe fit a simple mathematical model, the Richards model, to the number of excess laboratory-confirmed influenza cases in Mexico and Mexico City during the first 15 weeks in 2009 over the average influenza case number of the previous five baseline years of 2004-2008 during the same period to ascertain the turning point (or the peak incidence) of a wave of early influenza infections, and to estimate the transmissibility of the virus during these early months in terms of its basic reproduction number. The results indicate that there may have been an early epidemic in Mexico City as well as in all of Mexico during February/March. Based on excess influenza cases, the estimated basic reproduction number R0 for the early outbreak was 1.59 (0.55 to 2.62) for Mexico City during weeks 5–9, and 1.25 (0.76, 1.74) for all of Mexico during weeks 5–14.ConclusionsWe established the existence of an early epidemic in Mexico City and in all of Mexico during February/March utilizing the routine influenza surveillance data, although the location of seeding is unknown. Moreover, estimates of R0 as well as the time of peak incidence (the turning point) for Mexico City and all of Mexico indicate that the early epidemic in Mexico City in February/March had been more transmissible (larger R0) and peaked earlier than the rest of the country. Our conclusion lends support to the possibility that the virus could have already spread to other continents prior to the identification of the virus and the reporting of lab-confirmed pH1N1 cases in North America in April.

Predicting the level of vaccine-induced cross-immunity necessary to eliminate HIV epidemics composed of multiple subtypes

In a very interesting study, Kiwanuka et al. [1] report significant differences in the rates of transmission associated with different HIV-1 subtypes in Rakai, Uganda. Controlling for other factors, they find the transmission rate of subtype A to be nearly double that of subtype D. The authors suggest that differential transmission rates among subtypes are important for: (i) HIV vaccine development and testing, (ii) understanding the dynamics of HIV-1 epidemics in different geographical regions and (iii) projections of the pandemic. Over a decade ago, we constructed a mathematical model of an HIV epidemic composed of multiple co-circulating subtypes that differed on the basis of transmissibility [2]. We constructed this subtype model because preliminary data, collected in the mid 1990’s, indicated that HIV subtypes might exhibit differences in transmission efficiency [3,4]. We used our model to predict temporal trends in prevalence of co-circulating subtypes and the potential impact of prophylactic vaccines. Specifically, we investigated (theoretical) vaccines that would provide a degree of protection against infection by one subtype and induce cross-immunity against infection by another subtype. As the focus of our modeling work is so closely in line with the implications of [1], we now reexamine our subtype model using the remarkable data of Kiwanuka et al. in order to gain insights into current epidemiological patterns and predict the long-term outcome of mass vaccination against HIV in Uganda. In [2], we used the model to calculate basic reproductive numbers (R0) for each of the co-circulating subtypes. R0 represents the expected number of secondary infections caused by the introduction of one infectious individual into a completely susceptible population, and hence is a measure of fitness. Our modeling showed that, in the absence of vaccination, the subtype with the largest R0 will eventually outcompete and eliminate the other subtype. However, we found elimination would take over 100 years to occur and that the prevalence of the less-fit subtype could remain high for several decades. If subtype D emerged before subtype A in Uganda, our results could explain why the less-fit subtype D is currently more prevalent than subtype A and is slowly decreasing (71 to 63% from 1994 to 2002), whereas the prevalence of subtype A is slowly increasing (15 to 20% from 1994 to 2002) [5]. As Kiwanuka et al. point out, it is important to develop vaccines that are effective against several subtypes in order to control HIV epidemics. Our previous modeling has shown that mass vaccination could result in several long-term outcomes: (i) elimination of both subtypes, (ii) elimination of only one subtype, and (iii) persistence of both subtypes [2]. We showed that which outcome would occur depends on the R0’s, the vaccine coverage level, and three characteristics of the vaccine: take (i.e. the fraction of individuals for which the vaccine produces a protective immune response), degree of protection against one subtype, and the level of cross-immunity (i.e. degree of protection against the second subtype) [2]. The model was originally formulated to reflect transmission of HIV in a community of men who have sex with men. However, the model can be parameterized to reflect heterosexual transmission in Uganda because no significant differences between male-to-female and female-to-male transmission were observed in [1]. Doing so, we assume that the transmissibility of subtype A is approximately double that of subtype D [1] and that the average time to develop AIDS is 8 and 6.5 years, for subtypes A and D, respectively [6]. Figure 1 shows the long-term outcomes of mass vaccination given different levels of vaccine-induced cross-immunity, vaccine take and coverage. Calculations were made assuming the vaccine would provide an 80% degree of protection against infection by subtype A. It may be seen that even using this highly effective vaccine, HIV elimination will only be possible if a high fraction of the population is effectively vaccinated (Figure 1). For example, even if the vaccine take is 75%, it would be necessary to vaccinate over 90% of the population and for the vaccine to induce more than 30% cross-immunity against subtype D. If the level of cross-immunity is too low, elimination would not be possible and the less-fit subtype D could outcompete subtype A (Figure 1). This occurs when the vaccine’s protection renders subtype A less fit than subtype D. Fig. 1 Predicted long-term outcomes of a vaccination policy in Uganda using a vaccine with an 80% degree of protection against infection from subtype A. The fraction effectively vaccinated is calculated as the product of take and population coverage (e.g. if ... Our findings indicate that the presence of multiple subtypes will make HIV elimination more difficult and that mass vaccination campaigns may produce surprising results. Sincerely Dr. David J. Gerberry and Professor Sally Blower

Zero-Energy State in Graphene in a High Magnetic Field

The fate of the charge-neutral Dirac point in graphene in a high magnetic field H has been investigated at low temperatures (T approximately 0.3 K). In samples with small gate-voltage offset V0, the resistance R0 at the Dirac point diverges steeply with H, signaling a crossover to a state with a very large R0. The approach to this state is highly unusual. Despite the steep divergence in R0, the profile of R0 vs T in fixed H saturates to a T-independent value below 2 K, consistent with gapless charge-carrying excitations.

Stability of the director profile of a nematic liquid crystal around a spherical particle under an external field

We study numerically the effect of an external magnetic or electric field on the director profiles of a nematic liquid crystal around a spherical particle. We pay particular attention to the stability of a hyperbolic hedgehog defect accompanying the particle, which transforms into a Saturn-ring defect encircling the particle under a sufficiently strong external field. We focus on the particle size dependence of the two important threshold field strengths: the "thermodynamic-transition" field strength H1 at which the hedgehog and the Saturn-ring configurations have the equal free energy, and the critical field strength H2 at which the hedgehog loses its (meta)stability. Our numerical results demonstrate that while H1 is non-monotonically dependent on the particle radius R0, H2 monotonically increases with R0 and the dependence of H2 is weak for large R0. The non-monotonic dependence of H1 on R0 can be explained by comparing the energies of the two configurations and assuming the dependence of those energies on a rescaled field. A crude argument of the energetics of a hyperbolic hedgehog defect under an external field shows that for an asymptotically large R0 the critical field strength is independent of R0, which agrees with our numerical finding.

Optimizing boron implantation dose of HgCdTe infrared detectors

Using the material chip technology,large area photodiodes of n-on-p structure with different boron implantation dose are fabricated on the Hg1-xCdxTe film for mid-infrared wavelength region(x=0.291).Current-voltage characteristics of the photodiodes are measured at 77K and zero bias resistance-area products of different photodiodes are fitted from the data in the voltage range of -0.2—0.08V.The study indicated that the R0A products of different elements depended distinctly upon the implanted boron dose.A large R0 value has also obtained in another chip with x=0.2743.All the samples in this study are grown by Riber 32P molecular-beam epitaxy system and all the junctions-forming process is same to the standard planar technology but using a series of metallic masks during the boron ion implantation.

Electronic energy transfer between fluorescent dyes with inter- and intramicellar interactions

Energy transfer by dipole–dipole interaction between cationic dyes solubilized in micelles of sodium dodecyl sulfate (SDS) in aqueous solution was studied in the particular case where donor–acceptor Förster critical radius (R0) is larger than the micelle diameter (dm). Using the donor–acceptor dye pairs acridine/Nile blue (R0=68Å), and 9-aminoacridine/Nile blue (R0=36Å), long range interaction allows energy transfer from a survival isolated excited donor to an acceptor solubilized in a neighboring micelle. The efficiency of intramicellar energy transfer in steady-state measurements was proportional to the product of micelle concentration and average acceptor occupancy, being more pronounced in the case of the pair with large R0 value. In these situations with R0>dm, the distribution analysis of decay times recovers two well separated contributions where the short-lived components are related to fast intramicellar quenching, and the long-lived components are ascribed to long range intermicellar energy transfer.

On resonance and nonresonance interactions between electrons and spatially periodic clusters

The effects of resonance and nonresonance interactions between electrons and spherical structures with spatial periodicity in the radial direction (clusters) were studied. It was shown analytically and by numerical calculations that the δ l phase shift of the wave function, which arises in resonance electron scattering by such a periodic structure of a fairly large radius r0, was not small even at a small ratio between the U0 amplitude of the periodic potential and scattered electron energy E(e0=U0/E≪1) and equaled |δ l |=π/4 (modulo π). This phase shift corresponded to the limiting case of a large Born parameter for the cluster, ξ0=r0U0/ℏv≫1, where v is the characteristic velocity of the electron. The effect of nonresonance electron scattering by a periodic potential whose spatial period was incommensurate with the Brillouin wavelength of the scattered electron was considered analytically. The effect of nonresonance scattering was shown to be of a higher order in the e0≪1 parameter than resonance scattering. The cross section of electron scattering by a cluster was calculated, which allowed the conductivity of a medium containing clusters to be estimated.

Hydrocarbon Expulsion Threshold: Significance and Applications to Oil and Gas Exploration

Hydrocarbon explusion threshold (HET) is the critical condition for hydrocarbon expulsion in separate phase from a source rock when the generated hydrocarbon amount has satisfied all needs for absorption by minerals, solution in water, and blocking of capillary pressure. Research results show that the HET varies mainly with three geological parameters: total organic carbon content (C%), kerogen type index (KTI) and thermal maturation degree (R0). Source rocks with low C% and KTI cross the HET at a high level of maturation degree (larger R0); source rocks with lower R0 and C% can also cross the HET if the kerogen has a larger KTI. Under general geological conditions, a source rock first crosses the methane expulsion threshold (HETgl), then the heavy hydrocarbon gas threshold (HETgn), and finally the liquid hydrocarbon expulsion threshold (HET0). In this paper the concept of HET, and its critical conditions, are applied to establish the scientific validity of the concept and grade the source rocks, to study the phases of hydrocarbons in migration and the mechanisms of hydrocarbon accumulation, and to divide the hydrocarbon expulsion into stages. Applications to different basins in China show that HET provides an accurate and efficient method to guide oil and gas prospecting.