Showing papers by "Tata Institute of Fundamental Research published in 1999"

The Abelian sandpile and related models

Abstract: The Abelian sandpile model is the simplest analytically tractable model of self-organized criticality. This paper presents a brief review of known results about the model. The Abelian group structure of the algebra of operators allows an exact calculation of many of its properties. In particular, when there is a preferred direction, one can calculate all the critical exponents characterizing the distribution of avalanche-sizes in all dimensions. For the undirected case, the model is related to q → 0 state Potts model. This enables exact calculation of some exponents in two dimensions, and there are some conjectures about others. We also discuss a generalization of the model to a network of communicating reactive processors. This includes sandpile models with stochastic toppling rules as a special case. We also consider a nondashAbelian stochastic variant, which lies in a different universality class, related to directed percolation.

Electronic Spectra and Their Relation to the ( π,π) Collective Mode in High- Tc Superconductors

Abstract: The photoemission line shape near (pi, 0) in Bi(2)Sr(2)CaCu(2)O(8+delta) below T(c) is characterized by a sharp peak, followed at higher energy by a dip and hump. We study the evolution of this line shape as a function of momentum, temperature, and doping. We find the hump scales with the peak and persists above T(c) in the pseudogap state. We present strong evidence that the peak-dip-hump structure arises from the interaction of electrons with a collective mode of wave vector (pi, pi). The inferred mode energy and its doping dependence agree well with a magnetic resonance observed by neutron scattering.

The cosmic-ray proton and helium spectra between 0.4 and 200 gv

Abstract: We report on the hydrogen nuclei (protons and deuterons) spectrum from 0.15 to 200 GeV and on the helium nuclei spectrum over the energy range from 0.2 to 100 GeV nucleon~1 at the top of the atmo- sphere measured by the balloon-borne experiment Cosmic Antiparticle Ring-Imaging Cerenkov Experi- ment (CAPRICE), which was —own from Lynn Lake, Manitoba, Canada, on 1994 August 8¨9. We also report on the proton spectrum over the energy range from 0.15 to 4.2 GeV. The experiment used the NMSU-WiZard/CAPRICE balloon-borne magnet spectrometer equipped with a solid radiator Ring- Imaging Cerenkov (RICH) detector and a silicon-tungsten calorimeter for particle identi—cation. This was the —rst time a RICH was used together with an imaging calorimeter in a balloon-borne experiment. These detectors allowed for clear particle identi—cation, as well as excellent control of the detector effi- ciencies. The data were collected during 18 hr at a residual mean atmospheric depth of 3.9 g cm~2. With this apparatus 516,463 hydrogen and 32,457 helium nuclei were identi—ed in the rigidity range 0.4 to 200 GV and 1.2 to 200 GV, respectively. The observed energy spectrum at the top of the atmosphere can be represented by (1.1 ^ 0.1) ) 104 E~2.73B0.06 particles (m2 GeV sr s)~1 for hydrogen (E in GeV) between 20 and 200 GeV and (4.3 ^ 0.9) ) 102 E~2.65B0.07 particles (m2 GeV nucleon~1 sr s)~1 for helium nuclei (E in GeV nucleon~1) between 10 and 100 GeV nucleon~1. These spectra are in good agreement with other recent measurements above 10 GeV. The observed spectra —atten below 10 GeV due to solar modulation and are consistent with earlier measurements when solar modulation is taken into account. Between 5 and 200 GV the hydrogen to helium ratio as a function of rigidity was found to be approx- imately constant at 6.1 ^ 0.1. Subject headings: cosmic rayselementary particles

Superconducting gap anisotropy and quasiparticle interactions: A doping dependent photoemission study

Abstract: Comparing photoemission measurements on Bi2212 with penetration depth data, we show that a description of the nodal excitations of the d-wave superconducting state in terms of noninteracting quasiparticles is inadequate, and we estimate the magnitude and doping dependence of the Landau interaction parameter which renormalizes the linear T contribution to the superfluid density. Furthermore, although consistent with d-wave symmetry, the gap with underdoping cannot be fit by the simple coskx 2 cosky form, which suggests an increasing importance of long range interactions as the insulator is approached.

Giant radio sources

Abstract: We present multifrequency Very Large Array (VLA) observations of two giant quasars, 0437-244 and 1025-229, from the Molonglo Complete Sample. These sources have well-defined FR II radio structure, possible one-sided jets, no significant depolarization between 1365 and 4935 MHz and low rotation measure (\ RM \ < 20 rad m(-2)). The giant sources are defined to be those with overall projected size greater than or equal to 1 Mpc. We have compiled a sample of about 50 known giant radio sources from the literature, and have compared some of their properties with a complete sample of 3CR radio sources of smaller sizes to investigate the evolution of giant sources, and test their consistency with the unified scheme for radio galaxies and quasars. We find an inverse correlation between the degree of core prominence and total radio luminosity, and show that the giant radio sources have similar core strengths to smaller sources of similar total luminosity. Hence their large sizes are unlikely to be caused by stronger nuclear activity. The degree of collinearity of the giant sources is also similar to that of the sample of smaller sources. The luminosity-size diagram shows that the giant sources are less luminous than our sample of smaller sized 3CR sources, consistent with evolutionary scenarios in which the giants have evolved from the smaller sources, losing energy as they expand to these large dimensions. For the smaller sources, radiative losses resulting from synchrotron radiation are more significant while for the giant sources the equipartition magnetic fields are smaller and inverse Compton lass owing to microwave background radiation is the dominant process. The radio properties of the giant radio galaxies and quasars are consistent with the unified scheme.

The BPS spectra of gauge theories in two and four dimensions

Abstract: We study = (2,2) supersymmetric abelian gauge theories in two dimensions. The exact BPS spectrum of these models is shown to coincide with the spectrum of massive hypermultiplets of certain = 2 supersymmetric gauge theories in four dimensions. A special case of these results involves a surprising connection between four-dimensional = 2 SQCD with N colours and N$>Nf>N flavours at the root of the baryonic Higgs branch and the supersymmetric CP2N−Nf−1 σ-model in two dimensions. This correspondence implies a new prediction for the strong-coupling spectrum of the four-dimensional theory.

Projective Modules Over Polynomial Rings

Abstract: In 1976, Quillen [Q] and Suslin [Su 1] proved the following conjecture of Serre:-Conjecture: (Serre) Every finitely generated projective module over a polynomial ring k[T 1,..., T n ] over a field k is free.

Excited-State Kinetics of the Hydrophobic Probe Nile Red in Membranes and Micelles

Abstract: Nile red is a widely used hydrophobic dye for probing the structure, dynamics, and environment in many biological and microheterogeneous systems This paper reports emission-wavelength-dependent fluorescence intensity decay of Nile red in membranes and micelles Global analysis of these multiple fluorescence decays reveals a double-exponential decay with negative amplitudes for the short-lifetime component at longer emission wavelengths This indicates an excited-state kinetics leading to the formation of a new species in the excited state from the initially excited state In both the cases, the short lifetime corresponds to that of the initially excited species This excited-state kinetics is also observed in the case of viscous organic solvents such as 1-octanol and glycerol and is attributed to that of an excited-state solvent relaxation

Ring Diagram Analysis of Near-Surface Flows in the Sun

Abstract: Ring diagram analysis of solar oscillation power spectra obtained from Michelson Doppler Imager data is carried out to study the velocity fields in the outer part of the solar convection zone. The three-dimensional power spectra are fitted to a model that has a Lorentzian profile in frequency and includes the advection of the wave front by horizontal flows in order to obtain the two components of the subsurface flows as a function of the horizontal wave number and radial order of the oscillation modes. This information is then inverted using the optimally localized averages method and regularized least squares method to infer the variation in horizontal flow velocity with depth. The average rotation velocity at different latitudes obtained by this technique agrees reasonably with helioseismic estimates made using frequency-splitting data. The shear layer just below the solar surface appears to consist of two parts, with the outer part measuring up to a depth of 4 Mm where the velocity gradient does not show any reversal up to a latitude of 60°. In the deeper part the velocity gradient shows reversal in sign around a latitude of 55°. The zonal flow velocities inferred in the outermost layers appear to be similar to those obtained by other measurements. A meridional flow from equator poleward is found. It has a maximum amplitude of about 30 m s-1 near the surface, and the amplitude is nearly constant in the outer shear layer.

Spin-polarized tunneling in the half-metallic ferromagnets La 0.7-x Ho x Sr 0.3 MnO 3 (x=0 and 0.15): Experiment and theory

Abstract: The magnetoresistance (MR) in polycrystalline colossal magnetoresistive compounds follows a behavior different from single crystals below the ferromagnetic transition temperature. This difference is usually attributed to spin-polarized tunneling at the grain boundaries of the polycrystalline sample. Here we derive a theoretical expression for the contribution of spin-polarized tunneling to the magnetoresistance in granular ferromagnetic systems under the mean-field approximation. We apply this model to our experimental data on two half-metallic ferromagnets, ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ and ${\mathrm{La}}_{0.55}{\mathrm{Ho}}_{0.15}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ in the temperature range 5--300 K. We find that the theoretical predictions agree quite well with the observed dependence of the spin polarized MR on the spontaneous magnetization. We discuss the significance of our results in the light of the recent finding by A. Biswas et al. [Phys. Rev. B 59, 5368 (1999)] regarding the evolution of the total density of states at the Fermi level as a function of temperature in colossal magnetoresistive materials.

Mouth cancer in India: a new epidemic?

Abstract: Oral cancer has been traditionally described as a major form of cancer in India although on the basis of cancer registry data, it was thought that the incidence has decreased. There are several recent reports in the literature, however, predicting an increase in mouth cancer incidence in India. This prediction is based upon observation of an increasing prevalence of oral submucous fibrosis, especially in younger individuals, caused by gutka, an industrially manufactured food item. A comparison of the age distribution of recently reported oral submucous fibrosis cases and incident cases reported in the past clearly establishes that the disease is now occurring at much younger ages. A comparison of the age specific incidence rates of mouth cancer (ICD 143-5) during 1983-87 and 1995 in the city of Ahmedabad shows that the incidence has significantly increased in the younger population (< 50 years). Since tongue cancer (ICD 141) does not show a similar increase, it is concluded that the increase in mouth cancer incidence is real. Urgent public health measures are required to curb this new but avoidable epidemic.

Nmr observation of t-tetrads in a parallel stranded dna quadruplex formed by saccharomyces cerevisiae telomere repeats

Abstract: We report here the NMR structure of the DNA sequence d-TGGTGGC containing two repeats of Saccharomyces cerevisiae telomere DNA which is unique in that it has a single thymine in the repeat sequence and the number of Gs can vary from one to three. The structure is a novel quadruplex incor-porating T-tetrads formed by symmetrical pairing of four Ts via O4-H3 H-bonds in a plane. This is in contrast to the previous results on other telomeric sequences which contained more than one T in the repeat sequences and they were seen mostly in the flexible regions of the structures. We observed that the T4-tetrad was nicely accommodated in the center of the G-quadruplex, but it caused a small underwinding of the right handed helix. The T tetrad stacked well on the adjacent G3-tetrad, but poorly on the G5 tetrad. Likewise, T1 also formed a stable T-tetrad at the 5' end of the quadruplex. To our knowledge, this is the first report of T-tetrad formation in DNA structures. These observations are of significance from the points of view of both structural diversity and specific recognitions.

NMR studies on truncated sequences of human telomeric DNA: observation of a novel A-tetrad.

Abstract: The structure of the telomeric DNA has been a subject of extensive investigation in recent years due to the realization that it has important functional roles to play in vivo and the observations that truncated telomeric sequences exhibit a great variety of 3D structures in aqueous solutions. In this context, we describe here NMR structural studies on two truncated human telomeric DNA sequences, d-AG3T and d-TAG3 Ti n solutions containing K + ions. The G 3 stretches in both the oligonucleotides were seen to form parallelstranded quadruplexes. However, the AG3 segment as a whole, had different structural characteristics. The structure of d-AG3T revealed the formation of a novel A-tetrad, which was not seen in d-TAG 3 T. The A’s in the tetrad had syn glycosidic conformation as opposed to the anti conformation of the G’s in the G-tetrads. The A-tetrad stacked well over the adjacent G-tetrad and the twist angle at this step was smaller in d-AG 3 Tt han in d-TAG 3 T. These observations are expected to be significant from the point of view of structural diversity and recognition in telomeres.

Magnetic anisotropy, first-order-like metamagnetic transitions, and large negative magnetoresistance in single-crystal Gd 2 PdSi 3

Abstract: Electrical resistivity (\ensuremath{\rho}), magnetoresistance (MR), magnetization, thermopower, and Hall-effect measurements on the single-crystal ${\mathrm{Gd}}_{2}{\mathrm{PdSi}}_{3},$ crystallizing in an ${\mathrm{AlB}}_{2}$-derived hexagonal structure, are reported. The well-defined minimum in \ensuremath{\rho} at a temperature above N\'eel temperature ${(T}_{N}=21\mathrm{K})$ and large negative MR below $\ensuremath{\sim}{3T}_{N},$ reported earlier for the polycrystals, are reproducible even in single crystals. Such features are generally uncharacteristic of Gd alloys. In addition, we also found interesting features in other data, e.g., two-step first-order-like metamagnetic transitions for the magnetic field along [0001] direction. The alloy exhibits anisotropy in all these properties, though Gd is an $S$-state ion.

Brane constructions, fractional branes and anti-deSitter domain walls

Abstract: Compactifications of type IIB string theory on AdS5X5, where X5 is an Einstein space, can have one-fourth or half maximal supersymmetry for certain choices of X5. Some of these theories admit exotic domain walls arising from 5-branes wrapping 2-cycles in X5. We explore the relationship among these domain walls, fractional branes and branes stretched on intervals. World-volume fluxes in the wrapped branes play an important role in the analysis. We draw some parallels between the AdS background with exotic domain walls and = 1 supersymmetric MQCD, and identify other extended objects on the AdS side in the dual brane construction. The process of brane creation is used to give an alternate derivation of the relationship between fractional branes and branes on intervals.

Giant Radio Sources

Abstract: We present multi-frequency VLA observations of two giant quasars, 0437-244 and 1025-229, from the Molonglo Complete Sample. These sources have well-defined FRII radio structure, possible one-sided jets, no significant depolarization between 1365 and 4935 MHz and low rotation measure ($\mid RM \mid < 20 rad/m^2$). The giant sources are defined to be those whose overall projected size is $\geq$ 1 Mpc. We have compiled a sample of about 50 known giant radio sources from the literature, and have compared some of their properties with a complete sample of 3CR radio sources of smaller sizes to investigate the evolution of giant sources, and test their consistency with the unified scheme for radio galaxies and quasars. We find an inverse correlation between the degree of core prominence and total radio luminosity, and show that the giant radio sources have similar core strengths to the smaller sources of similar total luminosity. Hence their large sizes are unlikely to be due to stronger nuclear activity. The degree of collinearity of the giant sources is also similar to the sample of smaller sources. The luminosity-size diagram shows that the giant sources are less luminous than our sample of smaller-sized 3CR sources, consistent with evolutionary scenarios where the giants have evolved from the smaller sources losing energy as they expand to these large dimensions. For the smaller sources, radiative losses due to synchrotron radiation is more significant while for the giant sources the equipartition magnetic fields are smaller and inverse Compton losses with the microwave background radiation is the dominant process. The radio properties of the giant radio galaxies and quasars are consistent with the unified scheme.

Search for charged Higgs bosons in decays of top quark pairs

Abstract: We present a search for charged Higgs bosons in decays of pair-produced top quarks using 109.2{plus_minus}5.8 pb{sup {minus}1} of data recorded from p{ovr p} collisions at {radical}(s)=1.8 TeV by the D0 detector during 1992{endash}1996 at the Fermilab Tevatron. No evidence is found for charged Higgs production, and most parts of the [M{sub H{sup +}} {beta}] parameter space where the decay t{r_arrow}H{sup +}b has a branching fraction close to or larger than that for t{r_arrow}W{sup +}b are excluded at 95{percent} confidence level. Assuming m{sub t}=175 GeV and {sigma}(p{ovr p}{r_arrow} t{ovr t})=5.5 pb , for M{sub H{sup +}}=60 GeV , we exclude tan{number_sign}{beta}{lt}0.97 and tan{number_sign}{beta}{gt}40.9 . {copyright} {ital 1999} {ital The American Physical Society}

Triaxial projected shell model approach

Abstract: The projected shell model analysis is carried out using the triaxial Nilsson $+$ BCS basis. It is demonstrated that, for a better description of the moments of inertia of nuclei in the transitional region, it is necessary to take the triaxiality into account and perform the three-dimensional angular momentum projection from the triaxial Nilsson $+$ BCS intrinsic wave function.

Balloon measurements of cosmic ray muon spectra in the atmosphere along with those of primary protons and helium nuclei over midlatitude

Abstract: We report here the measurements of the energy spectra of atmospheric muons and of the parent cosmic ray primary proton and helium nuclei in a single experiment. These were carried out using the MASS superconducting spectrometer in a balloon flight experiment in 1991. The relevance of these results to the atmospheric neutrino anomaly is emphasized. In particular, this approach allows uncertainties caused by the level of solar modulation, the geomagnetic cut-off of the primaries and possible experimental systematics, to be decoupled in the comparison of calculated fluxes of muons to measured muon fluxes. The muon observations cover the momentum and depth ranges of $0.3--40 \mathrm{GeV}/c$ and $5--886 {\mathrm{g}/\mathrm{c}\mathrm{m}}^{2}$, respectively. A comparison of these results with those obtained in a previous experiment by the same collaboration using a similar apparatus allows us to search for differences due to the different experimental conditions at low energy and to check for the overall normalization between the two measurements. The proton and helium primary measurements cover the rigidity range from 3 to 100 GV, in which both the solar modulation and the geomagnetic cut-off affect the energy spectra at low energies. From the observed low-energy helium spectrum, the geomagnetic transmission function at mid-latitude has been determined.

Long-Term Scintillation Studies of Pulsars. I. Observations and Basic Results

Abstract: We report long-term scintillation observations of 18 pulsars in the dispersion measure range 3-35 pc cm-3 carried out from 1993 January to 1995 August using the Ooty Radio Telescope at 327 MHz. These observations were made with the aim of studying refractive effects in pulsar scintillation and obtaining reliable estimates of diffractive and refractive scintillation properties. Dynamic scintillation spectra of pulsars were regularly monitored at 10-90 epochs spanning 100-1000 days. Significant changes are observed in the dynamic spectra over timescales as short as a few days. Large-amplitude fluctuations are observed in quantities such as decorrelation bandwidth, scintillation timescale, drift rate, and flux density. Several pulsars show organized features, such as drifting bands in a highly pronounced manner. For some pulsars, gradual and systematic variations are seen in the drift rate of patterns that undergo several sign reversals during the observing time spans. Anomalous behavior, such as persistent drifts lasting over many months, is seen for PSRs B0834+06 and B1919+21. Four pulsars were studied for 2-4 well-separated observing sessions, each lasting over ~100 days. In some cases, significant variations are seen in the average scintillation properties and/or flux densities between successive observing sessions. From our data, we have been able to obtain more accurate and reliable estimates of scintillation properties and flux densities than those from the earlier observations by averaging out the fluctuations due to refractive scintillation effects. These measurements are used to derive parameters such as the strength of scattering and scintillation speeds. The scintillation speed estimates are found to be reasonably good indicators of proper-motion speeds of pulsars. The present measurements are compared with earlier measurements and the long-term stability of scintillation properties and flux densities is discussed.

Instantons and Chiral Anomaly in Fuzzy Physics

Abstract: In continuum physics, there are important topological aspects like instantons, theta-terms and the axial anomaly. Conventional lattice discretizations often have difficulties in treating one or the other of these aspects. In this paper, we develop discrete quantum field theories on fuzzy manifolds using noncommutative geometry. Basing ourselves on previous treatments of instantons and chiral fermions (without fermion doubling) on fuzzy spaces and especially fuzzy spheres, we present discrete representations of theta-terms and topological susceptibility for gauge theories and derive axial anomaly on the fuzzy sphere. Our gauge field action for four dimensions is bounded by the modulus of the instanton number as in the continuum.

Brane Constructions, Fractional Branes and Anti-deSitter Domain Walls

Abstract: Compactifications of type IIB string theory on AdS5 x X5, where X5 is an Einstein space, can have one-fourth or half maximal supersymmetry for certain choices of X5. Some of these theories admit exotic domain walls arising from 5-branes wrapping 2-cycles in X5. We explore the relationship among these domain walls, fractional branes and branes stretched on intervals. World-volume fluxes in the wrapped branes play an important role in the analysis. We draw some parallels between the AdS background with exotic domain walls and N=1 supersymmetric MQCD, and identify other extended objects on the AdS side in the dual brane construction. The process of brane creation is used to give an alternate derivation of the relationship between fractional branes and branes on intervals.

Different types of X-ray bursts from GRS 1915+105 and their origin

Abstract: We report X-ray observations of the Galactic X-ray transient source GRS 1915+105 with the pointed proportional counters of the Indian X-ray Astronomy Experiment (IXAE) onboard the Indian satellite IRS-P3, which show remarkable richness in temporal variability. The observations were carried out on 1997 June 12-29 and August 7-10, in the energy range of 2-18 keV and revealed the presence of very intense X-ray bursts. All the observed bursts have a slow exponential rise, a sharp linear decay, and broadly can be put in two classes: irregular and quasi-regular bursts in one class, and regular bursts in the other. The regular bursts are found to have two distinct timescales and to persist over extended durations. There is a strong correlation between the preceding quiescent time and the burst duration for the quasi-regular and irregular bursts. No such correlation is found for the regular bursts. The ratio of average flux during the burst time to the average flux during the quiescent phase is high and variable for the quasi-regular and irregular bursts, while it is low and constant for the regular bursts. We present a comprehensive picture of the various types of bursts observed in GRS 1915+105 in the light of the recent theories of advective accretion disks. We suggest that the peculiar bursts that we have seen are characteristic of the change of state of the source. The source can switch back and forth between the low-hard state and the high-soft state near critical accretion rates in a very short timescale, giving rise to the irregular and quasi-regular bursts. The fast timescale for the transition of the state is explained by invoking the appearance and disappearance of the advective disk in its viscous timescale. The periodicity of the regular bursts is explained by matching the viscous timescale with the cooling timescale of the postshock region. A test of the model is presented using the publicly available 13-60 keV RXTE/PCA data for irregular and regular bursts concurrent with our observations. It is found that the 13-60 keV flux relative to the 2-13 keV flux shows clear evidence for state change between the quiescent phase and the burst phase. The value of this ratio during burst is consistent with the values observed during the high-soft state seen on 1997 August 19, while its value during quiescent phase is consistent with the values observed during the low-hard state seen on 1997 May 8.

Sibling cell fate in the Drosophila adult external sense organ lineage is specified by prospero function, which is regulated by Numb and Notch

Abstract: Specification of cell fate in the adult sensory organs is known to be dependent on intrinsic and extrinsic signals. We show that the homeodomain transcription factor Prospero (Pros) acts as an intrinsic signal for the specification of cell fates within the mechanosensory lineage. The sensory organ precursors divide to give rise to two secondary progenitors - PIIa and PIIb. Pros is expressed in PIIb, which gives rise to the neuron and thecogen cells. Loss of Pros function affects the identity of PIIb and neurons fail to differentiate. Pros misexpression is sufficient for the transformation of PIIa to PIIb fate. The expression of Pros in the normal PIIb cell appears to be regulated by Notch signaling.

Inclusive jet cross section in p̄p collisions at √ = 1.8 TeV

Abstract: We have made a precise measurement of the central inclusive jet cross section at sqrt(s) = 1.8 TeV. The measurement is based on an integrated luminosity of 92 pb-1 collected at the Fermilab Tevatron pbar-p Collider with the D-Zero detector. The cross section, reported as a function of jet transverse energy (ET >= 60 GeV) in the pseudorapidity interval |eta| <= 0.5, is in good agreement with predictions from next-to-leading order quantum chromodynamics.

Influence of Dietary Factors on Oral Precancerous Lesions in a Population-Based Case-Control Study in Kerala, India

Abstract: BACKGROUND Although tobacco is the primary etiologic factor for oral precancerous lesions in India, evidence from other sources indicates that diet may modify risk. This case–control study was designed to minimize a variety of biases in its attempt to investigate the relation between diet and oral precancerous lesions. METHODS In a house-to-house survey of 5056 tobacco users in a rural area of Ernakulam district in Kerala, India, 226 individuals (44 females and 182 males) were found to have precancerous lesions (cases), which in 4 cases proved to be cancer. From among the examinees, an equal number of controls who were free of oral mucosal lesions and were matched to the cases regarding age (±5 years), gender, ward of residence, and use of tobacco also were enrolled. Dietary data were obtained using a customized interviewer-administered food-frequency questionnaire. All subjects and interviewers were blinded to the disease status of the subject. RESULTS After controlling for tobacco use, intake of fruits, vegetables, and β-carotene evinced inverse trends in risk (P < 0.05), with an average reduction of over 10% per quartile of exposure. Associations with certain micronutrients appeared to differ according to gender, with an apparent 20% reduction in risk per mg of zinc consumed per day among men and the suggestion of an increased risk among those women in the lowest quartile of iron intake (an increase of approximately 2.5-fold) and ascorbic acid intake (an increase of approximately 70% increase) compared with other women (P < 0.10). CONCLUSIONS Consumption of vegetables, fruits, and several micronutrients may inhibit precancerous lesions of the oral cavity. Cancer 1999;85:1885–93. © 1999 American Cancer Society.