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1.
Am J Health Behav ; 46(3): 324-336, 2022 06 23.
Artículo en Inglés | MEDLINE | ID: mdl-35794757

RESUMEN

Objective: Latinos disproportionately experience overweight/obesity (OWOB) and insufficient physical activity (PA), which are risk factors for numerous health conditions. Whereas numerous studies investigate acculturation as a determinant of OWOB and PA, few have examined acculturation multidimensionally, and none has examined its interaction with gender. Methods: Participants were 140 Latino adults. Primary outcomes were status as OWOB and endorsement of insufficient PA. Acculturation was measured with the Multidimensional Acculturation Scale II. Logistic regression analyses were used to examine the moderating effect of gender on the relationship between each acculturation scale and outcome, controlling for education, nativity, and smoking status. Results: Greater Spanish proficiency was significantly associated with lower odds of insufficient PA. Greater American Cultural Identity was significantly associated with higher odds of OWOB. Women had significantly higher odds of endorsing insufficient PA compared to men. Gender did not moderate the relationship between acculturation and either OWOB or PA. Conclusions: Acculturation is similarly associated with OWOB and insufficient PA for Latino men and women. Cultural identity may need to be considered to target OWOB interventions. Acculturation may be less important, and gender more important, to consider for appropriate targeting of PA interventions.


Asunto(s)
Aculturación , Hispánicos o Latinos , Escolaridad , Ejercicio Físico , Femenino , Humanos , Obesidad , Estados Unidos
2.
Health Psychol ; 41(2): 145-154, 2022 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-35157479

RESUMEN

OBJECTIVE: Negative affect is widely emphasized in behavior modification interventions. However, positive affect is associated with smoking cessation, physical activity, and healthy dietary habits and may be an important treatment target. Few studies have examined the relationship between positive affect and health behaviors among Latinos, who disproportionately experience modifiable health risk behaviors. This study examined the independent associations of positive affect and negative affect on modifiable health risk behaviors among Latino adults. METHOD: Data came from 432 persons who participated in one of two studies examining determinants of modifiable health risk behaviors among Latino adults. Primary outcomes were current smoking, at-risk drinking, insufficient physical activity, and insufficient fruit and vegetable consumption. Predictors were positive and negative affect as measured by the Positive and Negative Affect Schedule. Associations between positive and negative affect and health risk behaviors were examined using multiple logistic regression. RESULTS: Positive affect was associated with lower odds of insufficient physical activity and insufficient fruit and vegetable consumption and lower odds of engaging in multiple health risk behaviors. Negative affect was associated with higher odds of at-risk drinking and current smoking. CONCLUSIONS: Emphasis on increasing positive affect may be warranted for multiple health risk behavior interventions targeting Latinos. Intervention development efforts may also consider prioritizing positive affect for physical activity and dietary interventions, and negative affect for at-drinking and smoking cessation interventions. (PsycInfo Database Record (c) 2022 APA, all rights reserved).


Asunto(s)
Conductas de Riesgo para la Salud , Cese del Hábito de Fumar , Conductas Relacionadas con la Salud , Hispánicos o Latinos , Humanos , Fumar/epidemiología
3.
Am J Health Promot ; 36(3): 429-439, 2022 03.
Artículo en Inglés | MEDLINE | ID: mdl-34865517

RESUMEN

PURPOSE: Smoking and at-risk drinking are each associated with lower primary care utilization, but the influence of their co-occurrence is not known. The current study compared associations of endorsement of one behavior vs endorsement of both with primary care utilization. DESIGN: Cross-sectional telephone survey. SETTING: All United States and Territories. SUBJECTS: 246 801 adults aged 18-64. MEASURES: The outcome was endorsement of attending a past-year primary care visit. Predictor variables included drinking and smoking status examined individually and combined. ANALYSIS: Multivariable logistic regressions, adjusted for socio-demographics and number of chronic health conditions. RESULTS: The odds of attending a past-year primary care visit were 24% lower for persons who drank at risk levels compared to the odds of persons who did not drink and 36% lower for persons who smoked vs those who did not smoke. Among persons who endorsed at least one risk behavior, the odds of attending a past-year primary care visit were 25-35% lower for those who engaged in multiple behaviors compared to the odds of persons who engaged in one behavior. CONCLUSION: Substance use screening and intervention services in primary care may not be reaching individuals with the greatest need for services. Proactive outreach and identification of primary care utilization barriers are needed, with special consideration of those with co-occurring substance use.


Asunto(s)
Conductas Relacionadas con la Salud , Fumar , Adolescente , Adulto , Consumo de Bebidas Alcohólicas/epidemiología , Sistema de Vigilancia de Factor de Riesgo Conductual , Estudios Transversales , Humanos , Persona de Mediana Edad , Atención Primaria de Salud , Fumar/epidemiología , Estados Unidos/epidemiología , Adulto Joven
4.
Am J Drug Alcohol Abuse ; 48(1): 110-119, 2022 Jan 02.
Artículo en Inglés | MEDLINE | ID: mdl-34932409

RESUMEN

BACKGROUND: The existing research on affective and interpersonal determinants of smoking cessation largely under-represents minority smokers, such as Latinos. OBJECTIVE: The current study examined associations between affective and interpersonal factors with intermediary smoking cessation variables among Mexican-American smokers (N = 290; 60% male). METHODS: Measures of positive and negative affect, social support, and loneliness were each examined for associations with measures of motivational readiness to quit smoking, and smoking abstinence self-efficacy. Significant predictors were entered into models simultaneously to examine their unique associations. Covariates included gender, age, and educational attainment. RESULTS: Negative affect (b = .68, SE b = .14, p < .001) and loneliness (b = .20, SE b = .09, p < .05) were independently associated with motivation. Negative affect (b = .20, SE b = .06, p < .01) and positive affect (b = .34 SE b = .07, p < .001) were independently associated with self-efficacy. In the final models, only negative affect was associated with motivation (b = .68, SE b = .17, p < .001); whereas negative (b = .17, SE b = .06, p < .01) and positive (b = . 32, SE b = .07, p < .001) affect were associated with self-efficacy. CONCLUSION: Results highlight the importance of resilience factors (e.g., positive affect) among Mexican-American smokers. Cessation interventions regularly target negative affect among smokers; additional focus on positive affect in cessation interventions with this population may be warranted.


Asunto(s)
Fumadores , Cese del Hábito de Fumar , Femenino , Hispánicos o Latinos , Humanos , Soledad , Masculino , Americanos Mexicanos , Motivación , Autoeficacia , Fumar/psicología , Cese del Hábito de Fumar/métodos
5.
Am J Addict ; 30(5): 485-495, 2021 09.
Artículo en Inglés | MEDLINE | ID: mdl-34143567

RESUMEN

BACKGROUND AND OBJECTIVES: Screening, brief intervention, and referral to treatment (SBIRT) can reduce substance use, but receipt of these services by those who use cannabis frequently and have cannabis use disorder (CUD) remains unexplored. We examined cannabis use frequency and CUD's associations with the odds of receiving a substance use screening and a healthcare professional discussion among those who used healthcare services. METHODS: Data came from the 2015-2019 National Survey on Drug Use and Health (N = 214,505 aged 18+). Among adults who used cannabis and attended healthcare settings in the past year (N = 36,374), multivariable logistic regression analysis was used to examine associations of cannabis use frequency and CUD with receiving a substance use screen and substance use discussion by a healthcare professional. RESULTS: Cannabis use frequency was associated with higher odds of receiving a screen (adjusted odds ratio [AOR] = 1.27, 95% confidence interval [CI] = 1.14-1.41 for 300+ days of use) and a discussion among those screened (AOR = 1.83, 95% CI = 1.60-2.09 for 300+ days of use). CUD was not associated with receiving a screen, but it was positively associated with receiving a discussion among those screened (AOR = 1.22, 95% CI = 1.08-1.39). Nonmedical users were less likely to have a discussion among those screened and not screened. DISCUSSION AND CONCLUSIONS: Findings indicate disparities in screening and discussion of substance use with patients, especially between medical and nonmedical users. SCIENTIFIC SIGNIFICANCE: Study findings provide novel insight into differences in the reach of SBIRT services among adult cannabis users.


Asunto(s)
Cannabis , Alucinógenos , Abuso de Marihuana , Trastornos Relacionados con Sustancias , Adulto , Atención a la Salud , Humanos , Abuso de Marihuana/diagnóstico , Abuso de Marihuana/epidemiología , Trastornos Relacionados con Sustancias/epidemiología
6.
Drug Alcohol Depend ; 221: 108631, 2021 04 01.
Artículo en Inglés | MEDLINE | ID: mdl-33647587

RESUMEN

BACKGROUND: Despite significant geographical heterogeneity of sociodemographic and clinical characteristics, little is known about potential differences in cannabis use behaviors in U.S. geographic areas. In this study, we examined cannabis use behaviors in large metropolitan, small metropolitan, and nonmetropolitan areas. We focused on interactions between geographic areas and health insurance status and medical cannabis laws (MCL). METHODS: Data came from the 2015-2018 National Survey on Drug Use and Health (NSDUH; N = 171,766 adults; N = 36,175 cannabis users). Weighted chi-squares tests of independence and multivariable Poisson regression models were used to examine study questions. RESULTS: Past-year use was highest in large metropolitan areas (16.08 %). Frequent use was highest among nonmetropolitan area users (48.67 %). Uninsured adults had a higher likelihood of past-year use (RRR = 1.21, 95 % CI = 1.14, 1.29) and frequent use (RRR = 1.27, 95 % CI = 1.14, 1.41), but a lower likelihood of cannabis use disorder (RRR = 0.77, 95 % CI = 0.66, 0.89). Uninsured adults in nonmetropolitan areas had a higher likelihood (RRR = 1.62, 95 % CI = 1.39, 1.88) of past-year use than insured nonmetropolitan area adults. MCL state residency was associated with a higher likelihood of frequent use among nonmetropolitan (RRR = 1.39, 95 % CI = 1.11, 1.74) and small metropolitan users (RRR = 1.30, 95 % CI = 1.15, 1.47). Cannabis use disorder likelihood did not vary by geographic area. CONCLUSIONS: Lack of health insurance and MCL state residency are significant variables affecting cannabis use behaviors in small metropolitan and/or nonmetropolitan areas.


Asunto(s)
Uso de la Marihuana/epidemiología , Población Rural/estadística & datos numéricos , Población Suburbana/estadística & datos numéricos , Población Urbana/estadística & datos numéricos , Adolescente , Adulto , Control de Medicamentos y Narcóticos/estadística & datos numéricos , Femenino , Geografía , Encuestas Epidemiológicas , Humanos , Seguro de Salud/estadística & datos numéricos , Masculino , Uso de la Marihuana/legislación & jurisprudencia , Persona de Mediana Edad , Estados Unidos/epidemiología , Adulto Joven
8.
Nat Commun ; 10(1): 5494, 2019 12 02.
Artículo en Inglés | MEDLINE | ID: mdl-31792211

RESUMEN

LRIG1 has been reported to be a tumor suppressor in gastrointestinal tract and epidermis. However, little is known about the expression, regulation and biological functions of LRIG1 in prostate cancer (PCa). We find that LRIG1 is overexpressed in PCa, but its expression correlates with better patient survival. Functional studies reveal strong tumor-suppressive functions of LRIG1 in both AR+ and AR- xenograft models, and transgenic expression of LRIG1 inhibits tumor development in Hi-Myc and TRAMP models. LRIG1 also inhibits castration-resistant PCa and exhibits therapeutic efficacy in pre-established tumors. We further show that 1) AR directly transactivates LRIG1 through binding to several AR-binding sites in LRIG1 locus, and 2) LRIG1 dampens ERBB expression in a cell type-dependent manner and inhibits ERBB2-driven tumor growth. Collectively, our study indicates that LRIG1 represents a pleiotropic AR-regulated feedback tumor suppressor that functions to restrict oncogenic signaling from AR, Myc, ERBBs, and, likely, other oncogenic drivers.


Asunto(s)
Glicoproteínas de Membrana/metabolismo , Neoplasias de la Próstata/metabolismo , Receptores Androgénicos/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Animales , Línea Celular Tumoral , Regulación Neoplásica de la Expresión Génica , Humanos , Masculino , Glicoproteínas de Membrana/genética , Ratones Endogámicos NOD , Ratones SCID , Proteína Oncogénica p55(v-myc)/genética , Proteína Oncogénica p55(v-myc)/metabolismo , Neoplasias de la Próstata/genética , Unión Proteica , Receptor ErbB-2/genética , Receptor ErbB-2/metabolismo , Receptores Androgénicos/genética , Transducción de Señal , Proteínas Supresoras de Tumor/genética
9.
Transl Androl Urol ; 6(6): 1155-1158, 2017 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-29354504

RESUMEN

BACKGROUND: Pelvic pain is a common complaint, and management of it is often difficult. We sought to evaluate the utility of magnetic resonance imaging (MRI) in the diagnosis of male pelvic pain. Though MRIs are commonly ordered to evaluate pelvic pain, there are very few studies obtaining the efficacy of pelvic MRI in determining a definitive diagnosis. The primary aim of our study was to evaluate the clinical utility of pelvic MRI for a diagnosis code that included pain. METHODS: After receiving institutional review board approval, a retrospective study was performed of all pelvic MRIs completed at our institution from January 2, 2010 to December 31, 2014. These were further delineated into ordering providers by specialty and urology-specific International Classification of Diseases, Ninth Revision (ICD-9) code diagnoses (male pelvic pain, prostatitis, groin pain, scrotal pain, testicular pain, and penile pain). Clinical utility was defined as positive if MRI findings resulted in a change in management. Subanalysis was performed on patients with an ICD-9 co-diagnosis of previous oncologic concern. RESULTS: A total of 2,643 pelvic MRIs were ordered at our institution over a 5-year period. Of these, 597 pelvic MRIs (23%) were ordered for a diagnosis code that included pain (hip pain, rectal pain, joint pain, penile pain, scrotal pain, male pelvic pain and orchitis). Total utility for MRIs to find anatomic abnormalities potentially responsible for the present pain was 34% (205/597). When ordered by urologic providers, utility was 23%. Oncologists represented the highest positivity rate at 57%. CONCLUSIONS: Chronic pelvic pain is a multispecialty complaint that is difficult to treat. We were surprised to find the large number of both specialists and generalists invested in the management of pelvic pain. The increasing availability of MRI technology makes it a likely candidate to test for a clinically significant anatomic reason for pain. Though MRI is a test with minimal adverse effect and no increased risk of radiation exposure, the cost on the healthcare system should be offset by a clear clinical utility. We found total utility to be 34% across all ordering providers and an increase in positivity with concern of oncologic disease. Therefore, we would recommend pelvic MRIs in the evaluation of patients with refractory pelvic pain.

10.
Phys Rev Lett ; 117(15): 154502, 2016 Oct 07.
Artículo en Inglés | MEDLINE | ID: mdl-27768340

RESUMEN

The breakup and atomization of complex fluids can be markedly different than the analogous processes in a simple Newtonian fluid. Atomization of paint, combustion of fuels containing antimisting agents, as well as physiological processes such as sneezing are common examples in which the atomized liquid contains synthetic or biological macromolecules that result in viscoelastic fluid characteristics. Here, we investigate the ligament-mediated fragmentation dynamics of viscoelastic fluids in three different canonical flows. The size distributions measured in each viscoelastic fragmentation process show a systematic broadening from the Newtonian solvent. In each case, the droplet sizes are well described by Gamma distributions which correspond to a fragmentation-coalescence scenario. We use a prototypical axial step strain experiment together with high-speed video imaging to show that this broadening results from the pronounced change in the corrugated shape of viscoelastic ligaments as they separate from the liquid core. These corrugations saturate in amplitude and the measured distributions for viscoelastic liquids in each process are given by a universal probability density function, corresponding to a Gamma distribution with n_{min}=4. The breadth of this size distribution for viscoelastic filaments is shown to be constrained by a geometrical limit which can not be exceeded in ligament-mediated fragmentation phenomena.


Asunto(s)
Ligamentos , Sustancias Macromoleculares/química , Nebulizadores y Vaporizadores , Elasticidad , Reología , Viscosidad
11.
Phys Rev E ; 94(6-2): 067001, 2016 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-28085329

RESUMEN

Virot et al. [E. Virot et al., Phys. Rev. E 93, 023001 (2016)10.1103/PhysRevE.93.023001] assert that the critical wind speed at which ⩾50% of all trees in a population break is ≈42 m/s, regardless of tree characteristics. We show that empirical data do not support this assertion, and that the assumptions underlying the theory used by Virot et al. are inconsistent with the biomechanics of trees.

12.
Glob Chang Biol ; 21(8): 3021-35, 2015 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-25703827

RESUMEN

Wind is the major abiotic disturbance in New Zealand's planted forests, but little is known about how the risk of wind damage may be affected by future climate change. We linked a mechanistic wind damage model (ForestGALES) to an empirical growth model for radiata pine (Pinus radiata D. Don) and a process-based growth model (cenw) to predict the risk of wind damage under different future emissions scenarios and assumptions about the future wind climate. The cenw model was used to estimate site productivity for constant CO2 concentration at 1990 values and for assumed increases in CO2 concentration from current values to those expected during 2040 and 2090 under the B1 (low), A1B (mid-range) and A2 (high) emission scenarios. Stand development was modelled for different levels of site productivity, contrasting silvicultural regimes and sites across New Zealand. The risk of wind damage was predicted for each regime and emission scenario combination using the ForestGALES model. The sensitivity to changes in the intensity of the future wind climate was also examined. Results showed that increased tree growth rates under the different emissions scenarios had the greatest impact on the risk of wind damage. The increase in risk was greatest for stands growing at high stand density under the A2 emissions scenario with increased CO2 concentration. The increased productivity under this scenario resulted in increased tree height, without a corresponding increase in diameter, leading to more slender trees that were predicted to be at greater risk from wind damage. The risk of wind damage was further increased by the modest increases in the extreme wind climate that are predicted to occur. These results have implications for the development of silvicultural regimes that are resilient to climate change and also indicate that future productivity gains may be offset by greater losses from disturbances.


Asunto(s)
Cambio Climático , Modelos Teóricos , Pinus/crecimiento & desarrollo , Viento , Bosques , Nueva Zelanda
13.
Cell Cycle ; 13(11): 1798-810, 2014.
Artículo en Inglés | MEDLINE | ID: mdl-24732589

RESUMEN

15-Lipoxygenase-2 (15-LOX2) is a human-specific lipid-peroxidizing enzyme most prominently expressed in epithelial cells of normal human prostate but downregulated or completely lost in>70% of prostate cancer (PCa) cases. Transgenic expression of 15-LOX2 in the mouse prostate surprisingly causes hyperplasia. Here we first provide evidence that 15-LOX2-induced prostatic hyperplasia does not progress to PCa even in p53(+/-) or p53(-/-) background. More important, by generating 15-LOX2; Hi-Myc double transgenic (dTg) mice, we show that 15-LOX2 expression inhibits Myc-induced PCa development, such that in the 3-month- and 6-month-old dTg mice, there is a significant reduction in prostate intraneoplasia (PIN) and PCa prevalent in age-matched Hi-Myc prostates. The dTg prostates show increased cell senescence and expression of several senescence-associated molecules, including p27, phosphorylated Rb, and Rb1cc1. We further show that in HPCa, 15-LOX2 and c-Myc manifest reciprocal protein expression patterns. Moreover, RB1CC1 accumulates in senescing normal human prostate (NHP) cells, and in both NHP and RWPE-1 cells, the 15-LOX2 metabolic products 15(S)-HPETE and 15(S)-HETE induce RB1CC1. We finally show that unlike 15-LOX2, RB1CC1 is not lost but rather frequently overexpressed in PCa samples. RB1CC1 knockdown in PC3 cells enhances clonal growth in vitro and tumor growth in vivo. Together, our present studies provide evidence for tumor-suppressive functions for both 15-LOX2 and RB1CC1.


Asunto(s)
Araquidonato 15-Lipooxigenasa/metabolismo , Regulación Neoplásica de la Expresión Génica/fisiología , Hiperplasia Prostática/genética , Neoplasias de la Próstata/enzimología , Proteínas Tirosina Quinasas/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Animales , Araquidonato 15-Lipooxigenasa/genética , Proteínas Relacionadas con la Autofagia , Línea Celular Tumoral , Técnicas de Silenciamiento del Gen , Humanos , Inmunohistoquímica , Masculino , Ratones , Ratones Transgénicos , Proteínas Tirosina Quinasas/genética , Proteínas Proto-Oncogénicas c-myc/genética
14.
Appl Opt ; 51(12): 2212-22, 2012 Apr 20.
Artículo en Inglés | MEDLINE | ID: mdl-22534935

RESUMEN

It is shown that reflective liquid crystal on silicon (LCOS) spatial light modulator (SLM) based interconnects or fiber switches that use defocus to reduce crosstalk can be evaluated and optimized using a fractional Fourier transform if certain optical symmetry conditions are met. Theoretically the maximum allowable linear hologram phase error compared to a Fourier switch is increased by a factor of six before the target crosstalk for telecom applications of -40 dB is exceeded. A Gerchberg-Saxton algorithm incorporating a fractional Fourier transform modified for use with a reflective LCOS SLM is used to optimize multi-casting holograms in a prototype telecom switch. Experiments are in close agreement to predicted performance.

15.
Appl Opt ; 51(5): 659-68, 2012 Feb 10.
Artículo en Inglés | MEDLINE | ID: mdl-22330301

RESUMEN

A technique of cross talk mitigation developed for liquid crystal on silicon spatial light modulator based optical interconnects and fiber switches is demonstrated. By purposefully introducing an appropriate aberration into the system, it is possible to reduce the worst-case cross talk by over 10 dB compared to conventional Fourier-transform-based designs. Tests at a wavelength of 674 nm validate this approach, and show that there is no noticeable reduction in diffraction efficiency. A 27% spot increase in beam diameter is observed, which is predicted to reduce at longer datacom and telecom wavelengths.

16.
Qual Manag Health Care ; 18(2): 103-14, 2009.
Artículo en Inglés | MEDLINE | ID: mdl-19369853

RESUMEN

This article reports an intervention to improve the quality and safety of hospital patient care by introducing the use of pharmacy robotics into the medication distribution process. Medication safety is vitally important. The integration of pharmacy robotics with computerized practitioner order entry and bedside medication bar coding produces a significant reduction in medication errors. The creation of a safe medication-from initial ordering to bedside administration-provides enormous benefits to patients, to health care providers, and to the organization as well.


Asunto(s)
Sistemas de Medicación en Hospital , Robótica , Administración de la Seguridad , Difusión de Innovaciones , Procesamiento Automatizado de Datos , Humanos , Sistemas de Entrada de Órdenes Médicas , Errores de Medicación/prevención & control , Sistemas de Medicación en Hospital/economía , Sistemas de Medicación en Hospital/organización & administración , Calidad de la Atención de Salud
17.
Tree Physiol ; 28(1): 75-83, 2008 Jan.
Artículo en Inglés | MEDLINE | ID: mdl-17938116

RESUMEN

The finite element method of structural analysis was used to model the dynamic behavior of three 20-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees subjected to applied loading. Detailed measurements of stem and branch geometry were made for each tree, enabling the first-order branches of each tree to be represented as individual cantilever beams attached to the stem. Three values for branch modulus of elasticity (E) were assumed: 4, 5 and 6 GPa. For two trees with relatively large crown masses (175 and 250 kg), significantly improved estimates of natural frequency were obtained when the branches were modeled as separate cantilever beams rather than as a series of discrete masses attached to the stem. Closest agreement with the results from field sway tests was found when branch E was 4 GPa. Oscillations of individual branches contributed to the damping of tree oscillations--a phenomenon known as structural damping--with the contribution increasing as branch E decreased. When branch E was 4 GPa, the phase difference between the oscillation of the stem and that of some branches was almost 180 degrees. We applied a series of forces separately to the stem and branches of each tree and determined the mechanical transfer function for each loading case. These transfer functions were similar to the theoretical transfer function for a damped harmonic oscillator, but showed a smaller tree response at higher loading frequencies, particularly when branch E was 4 GPa. Branch structural properties, particularly modulus of elasticity, appear to be important in defining overall tree behavior under applied loading.


Asunto(s)
Pseudotsuga/fisiología , Árboles/fisiología , Simulación por Computador , Modelos Biológicos , Tallos de la Planta/fisiología , Vibración , Soporte de Peso
18.
Ann Bot ; 98(4): 765-75, 2006 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-16868003

RESUMEN

BACKGROUND AND AIMS: Although density-specific stiffness, E/rho, (where E is Young's modulus and rho is wood density) is often assumed constant by the elastic similarity model, and in determination of critical buckling height (H(crit)), few studies have tested this assumption within species. Here this assumption is tested for Pinus radiata growing across an environmental gradient, and theory is combined with data to develop a model of Young's modulus. METHODS: Analyses use an extensive series of environmental plots covering the range of climatic and edaphic conditions over which P. radiata is grown in New Zealand. Reduced major axis regression was used to determine scaling exponents between log-log plots of H(crit) vs. groundline diameter (D), and E/rho vs. D. Path analysis was used to identify significant direct and indirect (through stem slenderness) edaphic and climatic influences on E. KEY RESULTS: Density-specific stiffness exhibited 3-fold variation. As E/rho scaled positively with D, the exponent of 0.95 between H(crit) and D exceeded the assumed value of 0.67 under constant E/rho. The final path analysis model included mean air temperature in early autumn (T(aut)) and slenderness as significant (P < 0.05) positive direct influences on E. Tree leaf area index and T(aut) were indirectly associated with E through their significant (P < 0.05) positive direct relationship with stem slenderness. Young's modulus was most sensitive to T(aut), followed by stem slenderness then leaf area index, and the final model explained 76 % of the variance in E. CONCLUSIONS: The findings suggest that within species E/rho variation may influence H(crit) and the scaling exponent between D and H(crit) so important in assumptions regarding allometric relationships. The model presented may provide a useful means of determining variation in E, E/rho and H(crit) across environmental gradients.


Asunto(s)
Ecosistema , Pinus/anatomía & histología , Modelos Biológicos , Nueva Zelanda , Agua/metabolismo
19.
Tree Physiol ; 24(11): 1239-50, 2004 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-15339733

RESUMEN

Secondary xylem of woody plants has a large volumetric proportion of gas occupying spaces that would otherwise be filled with water. We examined whether these gas-filled voids have a mechanical role by either decreasing the fresh mass the tree must support (by replacing some of the water with gas) or by providing inexpensive filler to increase stem diameter (thereby increasing the second moment of area at the expense of the modulus of elasticity and modulus of rupture). Calculations from published data show that temperate softwood species (n = 26) average 18 and 50% gas by volume for sapwood and heartwood, respectively; temperate hardwood species (n = 31) average 26% gas by volume in both the sapwood and heartwood; and tropical species (n = 52) with mixed sapwood and heartwood have 18% gas by volume. In this paper, we develop equations to show how gas affects the mechanical behavior of tree stems, and describe model results to show how gas affects mechanical stability, based on mass and stem diameters for six 34-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees. For the same applied load, modeled stems in which the gas space was filled with water differed in their surface stresses by < 2% from modeled stems in the native state (partially gas-filled), indicating no practical benefit from a reduction in stem mass due to gas. A second modeling scenario compared the native state to stems in which gas was removed and stem diameters decreased (and material properties adjusted to concur with the increased wood density) to conserve mass. Removal of the gas-filled voids resulted in up to 41% higher surface stress for the same applied load, caused by a decrease in the second moment of area greater than the increase in modulus of elasticity. Trees with gas removed had higher modulus of rupture, but could withstand up to 14% lower maximum wind forces than trees in their native state, suggesting a biomechanical role for the gas if the model assumptions are valid. The gas content may, however, have evolved in response to pressures unrelated to biomechanics. We discuss some of its potential effects on sapwood physiology.


Asunto(s)
Tallos de la Planta/fisiología , Árboles/fisiología , Fenómenos Biomecánicos , Gases/análisis , Modelos Biológicos , Tallos de la Planta/química , Pseudotsuga/fisiología , Árboles/química , Viento
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