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Theoretical investigations on ferroelectric tunnel junctions (FTJs) with asymmetric electrodes and a composite barrier are presented. A large tunneling electroresistance effect exists for the Pt/SrTi03/BaTi03/SrRu03 junction; on the other hand, exchange of the dielectric and ferroelectric layer stacking sequence can seriously degrade the performance. These correlations are rationalized by the proposed concept of an asymmetry factor, defined as the ratio between the average barrier heights of FTJs for two opposite polarization orientations. We show that a large asymmetry factor is beneficial to FTJs. This work may provide a way to enhance the performance of FTJs by structure engineering.

Framingham心脏研究是享誉全球的心血管病学研究，自1948年起始至今已走过70多年的历程，为当代心血管病学、流行病学的发展做出了杰出的贡献。我们就Framingham心脏研究的背景、设计、历程、成果和贡献做一简要介绍与回顾。.

We report the first measurement of the absolute branching fraction of the inclusive decay$$\Lambda _c^+ \rightarrow K_S^0X$$Λc+→KS0X. The analysis is performed using an$$e^+e^-$$e+e-collision data sample corresponding to an integrated luminosity of 567 $$\hbox {pb}^{-1}$$pb-1taken at$$\sqrt{s}$$s= 4.6 GeV with the BESIII detector. Using eleven Cabibbo-favored$${\bar{\Lambda }}_c^-$$Λ¯c-decay modes and the double-tag technique, this absolute branching fraction is measured to be$${\mathcal {B}}(\Lambda _c^+ \rightarrow K_S^0X)=(9.9\pm 0.6\pm 0.4)\%$$B(Λc+→KS0X)=(9.9±0.6±0.4)%, where the first uncertainty is statistical and the second systematic. The relative deviation between the branching fractions for the inclusive decay and the observed exclusive decays is$$(18.7\pm 8.3)\%$$(18.7±8.3)%, which indicates that there may be some unobserved decay modes with a neutron or excited baryons in the final state.

By analyzing a data sample corresponding to an integrated luminosity of 2.93 fb^{-1} collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we measure for the first time the absolute branching fraction of the D^{+}→ημ^{+}ν_{μ} decay to be B_{D^{+}→ημ^{+}ν_{μ}}=(10.4±1.0_{stat}±0.5_{syst})×10^{-4}. Using the world averaged value of B_{D^{+}→ηe^{+}ν_{e}}, the ratio of the two branching fractions is determined to be B_{D^{+}→ημ^{+}ν_{μ}}/B_{D^{+}→ηe^{+}ν_{e}}=0.91±0.13_{(stat+syst)}, which agrees with the theoretical expectation of lepton flavor universality within uncertainty. By studying the differential decay rates in five four-momentum transfer intervals, we obtain the product of the hadronic form factor f_{+}^{η}(0) and the c→d Cabibbo-Kobayashi-Maskawa matrix element |V_{cd}| to be f_{+}^{η}(0)|V_{cd}|=0.087±0.008_{stat}±0.002_{syst}. Taking the input of |V_{cd}| from the global fit in the standard model, we determine f_{+}^{η}(0)=0.39±0.04_{stat}±0.01_{syst}. On the other hand, using the value of f_{+}^{η}(0) calculated in theory, we find |V_{cd}|=0.242±0.022_{stat}±0.006_{syst}±0.033_{theory}.

Background The aim of this study was to investigate the prevalence of epidemiologic and physician‐diagnosed pollen‐induced AR (PiAR) in the grasslands of northern China and to study the impact of the intensity and time of pollen exposure on PiAR prevalence. Methods A multistage, clustered and proportionately stratified random sampling with a field interviewer‐administered survey study was performed together with skin prick tests (SPT) and measurements of the daily pollen count. Results A total of 6043 subjects completed the study, with a proportion of 32.4% epidemiologic AR and 18.5% PiAR. The prevalence was higher in males than females (19.6% vs 17.4%, P = .024), but no difference between the two major residential and ethnic groups (Han and Mongolian) was observed. Subjects from urban areas showed higher prevalence of PiAR than rural areas (23.1% vs 14.0%, P

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) have a central role in follicle growth, maturation and oestrus, but no clear pathway in the seasonal oestrus of yak (Bos grunniens) has been found. To better understand the role of FSH and LH in seasonal oestrus in the yak, six yaks were slaughtered while in oestrus, and the pineal gland, hypothalamus, pituitary gland, and gonads were collected. Using real-time PCR and immunohistochemical assays, we determined the mRNA and protein expression of the FSH and LH receptors (FSHR and LHR) in these organs. The analysis showed that the FSHR mRNA expression level was higher in the pituitary gland tissue compared with LHR (p

The exclusive process e+e−→ΛΛ¯, with Λ→pπ− and Λ¯→p¯π+, has been studied at s=2.396 GeV for measurement of the timelike Λ electric and magnetic form factors, GE and GM. A data sample, corresponding to an integrated luminosity of 66.9 pb−1, was collected with the BESIII detector for this purpose. A multidimensional analysis with a complete decomposition of the spin structure of the reaction enables a determination of the modulus of the ratio R=|GE/GM| and, for the first time for any baryon, the relative phase ΔΦ=ΦE−ΦM. The resulting values are R=0.96±0.14(stat)±0.02(syst) and ΔΦ=37°±12°(stat)±6°(syst), respectively. These are obtained using the recently established and most precise value of the asymmetry parameter αΛ=0.750±0.010 measured by BESIII. In addition, the cross section is measured with unprecedented precision to be σ=118.7±5.3(stat)±5.1(syst) pb, which corresponds to an effective form factor of |G|=0.123±0.003(stat)±0.003(syst). The contribution from two-photon exchange is found to be negligible. Our result enables the first complete determination of baryon timelike electromagnetic form factors.

We present the first amplitude analysis of the decay D_{s}^{+}→π^{+}π^{0}η. We use an e^{+}e^{-} collision data sample corresponding to an integrated luminosity of 3.19 fb^{-1} collected with the BESIII detector at a center-of-mass energy of 4.178 GeV. We observe for the first time the W-annihilation dominant decays D_{s}^{+}→a_{0}(980)^{+}π^{0} and D_{s}^{+}→a_{0}(980)^{0}π^{+}. We measure the absolute branching fraction B(D_{s}^{+}→a_{0}(980)^{+(0)}π^{0^{(}+)},a_{0}(980)^{+(0)}→π^{+(0)}η)=(1.46±0.15_{stat}±0.23_{sys})%, which is larger than the branching fractions of other measured pure W-annihilation decays by at least one order of magnitude. In addition, we measure the branching fraction of D_{s}^{+}→π^{+}π^{0}η with significantly improved precision.

VLDLR gene was chosen as a candidate gene influencing abdominal fat trait and body weight due to previous studies in human and mouse. Herein, the objectives of this study were to identify genetic polymorphisms of duck VLDLR gene, and to analyze association between combined haplotypes and abdominal fat trait in Gaoyou domestic duck. A total of 207 individuals, including the elite reservation farm Gaoyou duck (FG, n = 50), the newly formed Gaoyou duck (NG, n = 54), the reserve area Gaoyou duck (AG, n = 50), and Hybrid duck (HY, n = 53) were used for study. In this paper, one genomic fragment was sequenced in all ducks encompassing a region from exon 14 to exon 16. Five single nucleotide polymorphisms (SNPs) and three insertions/deletions (indels) were identifi ed. Based on the above eight SNPs, 11 haplotypes were identified. Th e H1 was the most common haplotype in AG, FG, and HY populations, which occurred at a frequency of more than 41%. Statistical analysis indicated that four combined haplotypes were associated with body weight at 10 weeks (BW10) (P < 0.05) and abdominal fat percentage (AFP) (P < 0.01) in Gaoyou FG and AG joint population. Th is result suggested that the VLDLR gene could be a potential gene influencing abdominal fat trait and body weight and may be used in marker-assisted selection (MAS).

Many cases of liver carcinoma miss the opportunity of surgical treatment because of hidden onset and delayed diagnosis. In recent years, interventional treatment has gradually become a non-surgical method for treating liver carcinoma. To discuss the effects of oxaliplatin in combination with epirubicin in the treatment and its influence on prognosis, this study randomly selected 218 advanced primary liver carcinoma patients from Binzhou People’s Hospital, Binzhou, China and divided them into a control group (n=109) and an observation group (n=109). Patients in both groups were given interventional treatment. Patients in the control group were perfused with oxaliplatin, while patients in the observation group were perfused with oxaliplatin and epirubicin. The effectsat 6-month and 12-month survival rates were compared between the two groups. The results demonstrated that the overall effective rate and clinical benefit rate of the observation group were much higher than those of the control group (30.3% vs 11.9%; 79.8%; vs 44.3%) (P less than 0.05). The serum Alpha Fetal Protein (AFP) and Carcino Embryonie Antigen (CEA) levels of the observation group were much lower than those of the control group; the Karnofsky performance score of the observation group was much lower than that of the control group; the two differences had statistical significance (P less than 0.05). The 6-month survival rate of the observation group was 91.67%, higher than that of the control group (86.11%) (P0.05). The 12-month survival rate of the observation group was 83.33%, much higher than that of the control group (61.11%) (P less than 0.05). The difference of the incidence of adverse reactions between the two groups had no statistical significance (P0.05). Thus, it can be concluded that oxaliplatin in combination with epirubicin can improve survival quality, extend survival time, and decrease the serum AFP and CEA levels in the treatment of primary liver carcinoma, with definite effects but without aggravating toxic and side effects. Therefore, the therapy has important clinical value.

The purpose of this study was to compare single arc volumetric modulated arc therapy (VMAT) to intensity modulated radiotherapy (IMRT) for spine SBRT in terms of target coverage, organ at risk (OAR) sparing and delivery performance. VMAT plans with 91 control points (VMAT-91CP) were generated for 15 spine metastases patients previously treated with a nine-field IMRT technique. VMAT and IMRT plans were compared based on target coverage, maximum spinal cord dose, maximum plan dose and volume of normal tissue receiving 20% to 80% of the prescribed dose. Treatment delivery time and monitor units (MU) were measured to determine delivery efficiency. To assess the impact of arc discretization in the treatment planning system (TPS), the VMAT-91CP plans were modified by almost doubling the number of CPs (VMAT-181CP). Planned-to-delivered dose agreement for both techniques was assessed using two types of 3D detector arrays. VMAT-91CP target coverage was equivalent to IMRT while maintaining or improving spinal cord sparing. This was achieved without increasing the volume of normal tissue receiving low or intermediate dose levels. Planned-to-delivered dose agreement equivalent to IMRT was achieved with VMAT, but required decreasing the CP angular spacing from 4° to 2° (VMAT-181CP plans). On average, VMAT-181CP plans reduced delivery time by 53% compared to IMRT. Single-arc VMAT for spine SBRT improved delivery efficiency while maintaining target coverage and OAR sparing compared to IMRT. VMAT plans generated with a CP gantry angular spacing of 2° is recommended to avoid a discretization effect in the TPS and ensure acceptable planned-to-delivered dose agreement.

Summary To investigate the influence of testicular microlithiasis (TM) on the outcomes of in vitro fertilisation (IVF), we retrospectively reviewed the ultrasonography results of the TM patients who underwent IVF treatment in our hospital. They were classified as classic-TM (CTM) or limited-TM (LTM) comparing with patients without TM (Non-TM). Semen parameters, rates of fertilisation, normal fertilisation, good embryos and clinical pregnancy were analysed. The Non-TM group showed higher percentage of morphologically normal spermatozoa than the CTM or LTM group (4.08 ± 2.07 versus 3.40 ± 2.00 versus 3.04 ± 1.66, p = .003) while the other general semen parameters were comparable. The LTM group showed higher rate of fertilisation than the CTM group (85.10% versus 81.12%, p = .044). Moreover, the rates of normal fertilisation of Non-TM (62.47%) and LTM (66.32%) group were significantly higher than the CTM (58.02%) group (p = .027 and p = .001 respectively). There were 333 embryo transfer cycles in total (including 222 fresh and 111 frozen). The overall clinical pregnancy rate was 54.95%, 58.33% and 64.12% in the group of CTM, LTM and Non-TM respectively. However, no statistically significant difference was obtained (p = .326). Our results suggest that TM may have influence on the IVF outcomes. The extent of microlithiasis correlates inversely with the rates of fertilisation and normal fertilisation.

The 15-nm-thickness BaTiO 3 (BTO) epitaxial film was prepared on the Nb-doped SrTiO 3 (NSTO) single crystal substrate using pulsed laser deposition technique. The morphology and structure of the film was measured by the AFM, TEM and XRD, respectively. The current–voltage curves show abnormal backward diode-like rectifying behavior at room temperature, which was discussed using the Schottky barrier model taking into account the movement of oxygen vacancies. The leakage currents under reverse bias were excellently fitted by the Poole–Frenkel (P–F) emission and Fowler–Nordheim (F–N) tunneling mechanisms, respectively. At forward bias, the current was fitted by the space-charge-limited current mechanism. The C–V curves indicate that there is a positive build-in voltage (about 0.56 V) in the Pt/BTO/NSTO structure, which confirms the backward rectifying behavior.

The effects of eleven different peat-containing substrates on growth, yield and fruit quality of cucumbers (Cucumis sativus L.) were studied in an eco-organic type soilless culture system during a 17-week greenhouse experiment. The results showed that physical characteristics of all substrates were within acceptable ranges of plant growth and development, but pH and EC values were beyond the optimal ranges when coal ash was over 25% in the mixture. The best seedling performance was obtained in the mixture of peat to coal ash 3:1 (T3), followed by 1:1 peat/coal ash (T6), 1:1:1 peat/vermiculite/coal ash (T8), and 3:1 peat/perlite (T2) treatment. Highest cucumber yield and fruit quality were obtained by the mixture of peat to vermiculite 1:1 (T4). And plants grown in 3:1 peat/vermiculite (T1), 3:1 peat/perlite (T2), 3:1 peat/coal ash (T3) had better yield than in 100% peat. The results indicate that addition of vermiculite, perlite and coal ash to peat resulted in a better seedling growth, higher yield and better quality of fruit probably owing to increasing water-holding capacity and aeration of peat, which demonstrates that inorganic substances such as vermiculite, perlite and coal ash could partially replace peat.

Since Baade's photographic study of M32 in the mid 1940s, it has been accepted as an established fact that M32 is a compact dwarf satellite of M31. The purpose of this paper is to report on the findings of our investigation into the nature of the existing evidence. We find that the case for M32 being a satellite of M31 rests upon Hubble Space Telescope (HST) based stellar population studies which have resolved red-giant branch (RGB) and red clump stars in M32 as well as other nearby galaxies. Taken in isolation, this recent evidence could be considered to be conclusive in favour of the existing view. However, the conventional scenario does not explain M32's anomalously high central velocity dispersion for a dwarf galaxy (several times that of either NGC 147, NGC 185 or NGC 205) or existing planetary nebula observations (which suggest that M32 is more than twice as distant as M31) and also requires an elaborate physical explanation for M32's inferred compactness. Conversely, we find that the case for M32 being a normal galaxy, of the order of three times as distant as M31, is supported by: (1) a central velocity dispersion typical of intermediate galaxies, (2) the published planetary nebula observations, and (3) known scaling relationships for normal early-type galaxies. However, this novel scenario cannot account for the high apparent luminosities of the RGB stars resolved in the M32 direction by HST observations. We are therefore left with two apparently irreconcilable scenarios, only one of which can be correct, but both of which suffer from potentially fatal evidence to the contrary. This suggests that current understanding of some relevant fields is still very far from adequate., Comment: 17 pages, 3 Postscript figures, uses cjaa.cls and natbib.sty (published version has 16 pages)

Ba 0.65 Sr 0.35 TiO 3 (BST) thin films have been deposited by radio frequency magnetron sputtering. The effects of the deposition parameters on the crystallization and microstructure of BST thin films were investigated by X-ray diffraction and field emission scanning electron microscopy, respectively. The crystallization behaviour of the films is clearly affected by the substrate temperature, annealing temperature, and sputtering pressure. The thin films that are deposited at room temperature are amorphous in their as-deposited state. However, an improved crystallization can be observed for BST thin films deposited at higher temperatures. As the annealing temperature is increased, the dominant X-ray diffraction peaks become sharper and more intense. The dominant diffraction peaks increase with sputtering pressure, steadily increasing for films deposited from 0.37 to 1.2 Pa. When the sputtering pressure is increased up to 3.9 Pa, the films have a (110) + (200) preferred orientation. Possible correlations between the crystallization and the changes in the sputtering pressure are discussed. SEM measurements indicate that the films, which consist of small grains, are smooth and that the interface between the film and the substrate is sharp and clear.

Ba0.65Sr0.35TiO3 (BST) thin films on p-silicon substrates were deposited by radio frequency magnetron sputtering. The effects of the deposition parameters on the crystallization and microstructure of BST thin films were investigated by X-ray diffraction and filed emission electron microscopy, respectively. The crystallization behavior of these films was apparently affected by the substrate temperature, annealing temperature and sputtering pressure. The improved crystallization can be observed for BST thin films that deposited at higher temperature. The dominant X-ray diffraction peaks became sharper and more intense as the annealing temperature increased. BST thin films deposited at high sputtering pressure of 3.9 Pa exhibited the (110) + (200) preferred orientation. Possible correlations of the crystallization with the sputtering pressure were discussed. The SEM morphology indicated the film was small grains and smooth.

Ba0.65Sr0.35TiO3 (BST) thin films have been prepared by radio frequency magnetron sputtering on fused quartz at different substrate temperatures. Optical constants (refractive index n, extinction coefficient k) were determined from the optical transmittance spectra using the envelope method. The dispersion relationship of the refractive index vs. substrate temperature was also investigated. The refractive index of BST thin films increased from 1.778 to 1.961 (at λ = 650 nm) as deposited temperature increases from 560°C to 650°C. The extinction coefficient of as-deposited BST thin films increased with the increase of the oxygen-to-argon ratio, which was due to the change of the film stoichiometry, structure, and texture of BST thin films. The oxygen-to-argon ratio also affected the fluorescence spectra. The fluorescence peaks intensity was greatly increased, apparent frequency shift was detected, and the linewidth became narrow as the ratio of oxygen to argon increased from 1:4 to 1:1. The fluorescence spectra also indicated the band transition of BST thin films was an indirect gap transition.

Ba"0"."6"5Sr"0"."3"5TiO"3 (BST) thin films doped with holmium were prepared on silicon and fused quartz substrates by a modified sol-gel technique. The microstructures of BST films were characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). The results showed that 3mol% Ho-doped BST has the largest grain size and surface root-mean square roughness. The transmission spectra of Ho-doped BST films were measured by spectrophotometer. The refractive index and thickness of 1mol% Ho-doped BST film was calculated using envelope method from the transmission spectra. It showed that the refractive index increased from 1.94 to 2.09 as wavelength decreased from 700nm to 400nm, which was smaller than pure BST thin films we have reported. The average oscillator strength and wavelength were estimated using a Sellmeir-type dispersion equation. These results show the potential of using Ho-doped BST thin films as an electro-optical novel material.

It was proved that higher haematocrit (Hct) might improve the function of brain after hypothermia circulation arrest (HCA). In the present study we established a new rat HCA model and investigated whether retrograde cerebral perfusion of oxygenated, compacted red blood cells (RBC) could attenuate brain injury after HCA.A new rat HCA model was developed and rats were randomly distributed into three groups: HCA group, HCA combined with retrograde cerebral perfusion of oxygenated, compacted red blood cell group (HCArcp group), and sham operation group (sham op. group). Animals both in the HCA group and in the HCArcp group underwent HCA 90 min at 18 degrees C. Brain damage after HCA was evaluated with light microscopy and electron microscopy. Immunohistochemistry and RT-PCR techniques were used to measured the different expressions of the C-Fos, Bcl-2, Bax mRNA and protein among the groups. Additionally we measured the wet/dry ratio of the brain in order to evaluate the oedema degree after HCA.The new HCA model of rat we developed was comparable to the clinical setting not only in terms of the intubation, anaesthesia method and materials employed but also in terms of the priming volume in relation to body weight. The number of injured neurones in the hippocampus CA1 and parietal cortex, but not in the thalamus of the HCA group, was significantly greater than that of the HCArcp group (P0.05). The mean score of mitochondrion of the hippocampus CA1 in the HCA group was significantly higher than in the HCArcp group (P0.05). The expression of C-Fos, Bax mRNA and protein in the hippocampus CA1 and/or parietal cortex area was higher in the HCA group than in the HCArcp group (P0.05). Expression of the mRNA and protein of Bcl-2 was higher in the HCArcp group than in the HCA group (P0.05). The degree of oedema after HCA between the HCA group and HCArcp group had no significant difference (P0.05).We established a new rat model of HCA comparable to the clinical setting. Retrograde cerebral perfusion of oxygenated, compacted RBC is a simple, effective, and safe method to protect the brain during HCA. Adjusting the gene expression in relation to apoptosis might contribute to the neuroprotective effects of a retrograde cerebral infusion of oxygenated, compacted RBC.

The Ba0.65Sr0.35TiO3 thin films have been prepared by the sol-gel method on fused quartz and (1102)- oriented Al2O3 substrates. The crystallization behavior and structure characterization were studied at different annealing temperatures by XRD and SEM. The as-fired thin films were found to be amorphous, and the films crystallized to a perovskite structure after a post-deposition annealing at 700 °C for 1 h in air. The grain of BST film was evenly distributed, indicating the sol-gel-derived Ba0.65Sr0.35TiO3 thin film has a well-defined microstructure. The refractive index increased from 2.16 to 2.35 as wavelength decreased from near infrared range (1000 nm) to visible range (430 nm). The energy gap of BST films deposited on Al2O3 substrate was found to be around 3.48 eV of indirect-transition type.

In this article, we report on the laser-induced formation of both C49 and C54 TiSi 2 films with fine grains using Q-switched Nd : YAG laser irradiation from Ti/Si samples. The films formed were characterized with micro-Raman spectroscopy, high-resolution transmission electron microscopy, energy-dispersive spectrometry and atomic force microscopy. The TiSi 2 films synthesized are single-phased and thin, with fine grains and a smooth film/substrate interface on the atomic scale. The process is likely to proceed via a solid-state reaction rather than liquid-phase intermixing. Our results demonstrate the unique advantages of a laser annealing technique and its potential in deep submicron semiconductor technology.

Germanium nanocrystals immersed in amorphous SiO x matrix have been synthesized by r.f. co-sputter deposition of Ge and quartz with post-growth annealing at 600-900 °C. The structures of the Ge nanocrystals and SiO x matrix have been studied with x-ray diffraction, high-resolution transmission electron microscopy and XPS depth profiling. Broad-band photoluminescence spectra have been observed from samples annealed at temperatures higher than 600°C. Possible photoluminescence mechanisms have also been discussed.

We compared the effects of glial cell line-derived neurotrophic factor (GDNF) on dorsal root ganglion (DRG) sensory neurons to that of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin 3 (NT-3). All of these factors were retrogradely transported to sub-populations of sensory neuron cell bodies in the L4/L5 DRG of neonatal rats. The size distribution of 125I-GDNF-labeled neurons was variable and consisted of both small and large DRG neurons (mean of 506.60 μm2). 125I-NGF was preferentially taken up by small neurons with a mean cross-sectional area of 383.03 μm2. Iodinated BDNF and NT-3 were transported by medium to large neurons with mean sizes of 501.48 and 529.27 μm2, respectively. A neonatal, sciatic nerve axotomy-induced cell death model was used to determine whether any of these factors could influence DRG neuron survival in vivo. GDNF and NGF rescued nearly 100% of the sensory neurons. BDNF and NT-3 did not promote any detectable level of neuronal survival despite the fact that they underwent retrograde transport. We examined the in vitro survival-promoting ability of these factors on neonatal DRG neuronal cultures derived from neonatal rats. GDNF, NGF, and NT-3 were effective in vitro, while BDNF was not. The range of effects seen in the models described here underscores the importance of testing neuronal responsiveness in more than one model. The biological responsiveness of DRG neurons to GDNF in multiple models suggests that this factor may play a role in the development and maintenance of sensory neurons. © 1997 John Wiley & Sons, Inc. J Neurobiol 32: 22–32, 1997.

SummaryTo examine the possibility of interspecies transmission and genetic reassortment of influenza viruses on farms in Southern China, we surveyed 20 farm families living outside the city of Nanchang who raised pigs and ducks in their homes. Weekly interviews of family members and virus isolation studies of throat swabs and faecal samples, collected from September 1992 to September 1993, established the seasonal pattern of respiratory tract infections in these families and identified 11 influenza viruses (6 in humans and 5 in ducks). Most of the human isolates were type A of H3N2 subtype. Serologic studies of farm pigs indicated infection by the same human viruses circulating in family members, but there was no evidence that either swine or avian viruses had been transmitted to pigs. Eight of 156 human serum samples inhibited the neuraminidase activity of two of the duck isolates, raising the possibility of interspecies transmission of these avian viruses. Genotype analysis of duck and human isolates provided no evidence for reassortment. Our findings support the concept that intermingling of humans, pigs and ducks on Chinese farms is favourable to the generation of new, potentially hazardous strains of influenza virus.

The three last pandemic strains of influenza A virus-Asian/57, Hong Kong/68 and Russian/77-are believed to have originated in China. The strains responsible for the 1957 and 1968 human pandemics were reassortants incorporating both human and avian influenza viruses, which may have arisen in pigs. We therefore undertook a population-based study in the Nanchang region of Central China to establish the prevalence, types and seasonal pattern of human influenza infection and to screen serum samples from animals and humans for evidence of interspecies transmission of influenza viruses. Two definite influenza seasons were demonstrated, one extending from November to March and the other July to September. The profile of antibodies to commonly circulating human influenza viruses was no different in Nanchang and neighboring rural communities than in Memphis, Tennessee, USA. In particular, Chinese women who raised pigs in their homes were no more likely to have been exposed to influenza virus than were subjects who seldom or never had contact with pigs. However, we did obtain evidence using isolated H7 protein in an enzyme-linked immunoabsorbent assay for infection of pig farmers by an avian H7 influenza virus suggesting that influenza. A viruses may have been transmitted directly from ducks to humans. The results of the serological survey also indicated that pigs in or near Nanchang were infected by human H1N1 and H3N2 influenza viruses, but not with typical swine viruses. We found no serological evidence for H2 influenza viruses in humans after 1968.