Frequency and variability of missing tree rings along the stems of Pinus halepensis and Pinus pinea from a semiarid site in SE Spain     

K. Novak  M. de Luis  K. ?ufarJ. Raventós 《Journal of Arid Environments》2011,75(5):494-498

We studied the occurrence of missing rings (MR) around and along the stems of three Pinus halepensis and three Pinus pinea trees growing in a semiarid Mediterranean site in SE Spain. Tree-ring analyses were performed along 8 radii on stem discs taken at 1 m distances from the base to the top of the trees. The tree rings analysed showed that 19% were missing in P. halepensis and 10% in P. pinea. MR were recorded in 61% of P. halepensis and 24% of P. pinea in the years analysed. Dry conditions from January to May and high late winter to spring temperatures seem to be the main climatic elements promoting MR in both species. In our research into P. halepensis, the frequency of MR gradually decreased from the bottom upward, but no such pattern was observed in P. pinea. Most tree rings were missing only locally (LMR), indicating that wood formation occurred every year in at least some part of a tree, and the tree rings were often discontinuous around and along the stem. Since the frequency of LMR greatly varies around and along the stem, our results suggest that serial sectioning along the stem provides more information on wood formation and responses of trees to environment than studying the samples at breast height only. The disadvantage of the technique is that, as in our study case, research is based on a limited sample size, since it requires destructive sampling with tree felling, which is not usually possible or desirable on highly vulnerable semiarid forest ecosystems.  相似文献   

Glacio-lacustrine stratigraphy,aquifer characterization and contaminant transport: a case study in South Lake Tahoe,California, USA     

Craig W. Morgan  Graham M. Kent  Gordon G. Seitz  Michaela Novak 《Hydrogeology Journal》2008,16(5):981-994

A hydrogeologic model that has been used by many researchers and consultants to describe an area of South Lake Tahoe, California, USA impacted by MTBE contamination describes a relatively homogeneous unconfined aquifer comprised of poorly sorted glacial outwash deposits, within which water-supply wells are able to exert significant alteration in natural groundwater flow. A re-examination of the area’s hydrogeology is presented, which supports a layered heterogeneous aquifer system constructed of alternating fine and coarser-grained glacio-lacustrine depositional units. This re-evaluation was accomplished through a review of lithologic logs across an area of approximately 1 km², combined with observations of significant hydraulic head differences and knowledge of the depositional environments controlled by Pleistocene Lake Tahoe high stands. Many of the fine-grained units observed at depths from 6 to 15 m, although relatively thin, are generally continuous and serve as significant barriers to groundwater flow. The vertical migration of contamination across these fine-grained units to deeper groundwaters was facilitated by cross-screened monitoring wells installed as part of site investigation activities. This conclusion highlights the importance of geologic characterization and proper monitoring well construction at contaminated site investigations.

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Electronic supplementary material   The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Michaela NovakEmail:

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Investigation of Reductive Dechlorination Supported by Natural Organic Carbon   总被引：1，自引：0，他引：1  

Heather V. Rectanus  Mark A. Widdowson  Francis H. Chapelle  Catherine A. Kelly  John T. Novak 《Ground Water Monitoring & Remediation》2007,27(4):53-62

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Uplift in seismic response of pile supported buildings     

L. El Hifnawy  M. Novak 《地震工程与结构动力学》1986,14(4):573-593

To resist seismic overturning moments piles are often designed for tensile forces which require pile connection to the cap and sometimes, socketing. For typical buildings, this paper theoretically examines the effect of these measures on seismic response, forces and pile loading in dependence on pile numbers, configuration and tip conditions.  相似文献   

Dynamic soil-structure interaction,John P. Wolf,Prentice-Hall,Englewood Cliffs,N.J., 1985. No. of pages: £466. Price: £61.45     

M. Novak 《地震工程与结构动力学》1986,14(6):951-951

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Micrometeorological changes associated with vegetation removal and influencing desert formation     

M. D. Novak 《Theoretical and Applied Climatology》1990,42(1):19-25

Summary The effects of vegetation removal on the energy balance components, soil and air temperatures, and atmospheric vapour densities are predicted using a recently developed analytical theory. The results show that the sum of daily average sensible and latent heat flux densities decreases as the surface resistance and albedo increase and the surface roughness decreases, which according to some numerical models implies reductions in rainfall. For a dry surface daytime atmospheric heating decreases with vegetation removal because albedo and soil admittance increase and atmospheric admittance decreases; according to another model this should reduce precipitation. The results show that surface temperature is not an appropriate diagnostic measure of sensible heat flux density, even under constant meteorological conditions, when changes in surface roughness also occur. Analysis of some surface temperatures measurements made in the Negev and the Sinai suggests that understanding the turbulent processes occurring in the roughness sublayer, when the surface is partially covered with vegetation, is critical in assessing the micrometeorological changes associated with vegetation removal and desert formation.With 2 Figures  相似文献   

Dynamic behaviour of turbine-generator-foundation systems     

Weiming Liu  Milos Novak 《地震工程与结构动力学》1995,24(3):339-360

In this paper a comprehensive investigation on the dynamic characteristics of turbine–generator–foundation systems is performed. All the major components of the system, including turbine–generator casing, shaft, rotors, journal bearings, deck, piers, foundation mat, piles, and soil medium, have been included. Full interaction between the turbine–generator set, the foundation superstructure, and the soil medium, is considered. A hybrid method is used to establish the mathematical model for the turbine–generator-foundation system. The analysis is conducted in the frequency domain through complex frequency response analysis. The response in the time domain is obtained by Fourier transform. The seismic excitation is represented as the control motion on the ground surface, which is generated as an artificial earthquake. A 300 MW turbine-generator-foundation system is analysed under excitations from rotor unbalances and earthquakes. The influence of turbine-generator casing and soil anisotropy on the response of the system is explored. It is found that the presence of casing and soil anisotropy strongly influences the displacements and internal forces of the system under rotor unbalance excitation. Under seismic excitation, however, although the presence of casing and soil anisotropy does affect the displacements of the system, their effect on the internal forces of the system is minimal.  相似文献   

Soil-pile interaction in vertical vibration     

T. Nogami  M. Novak 《地震工程与结构动力学》1976,4(3):277-293

The interaction between a soil layer and an end bearing pile is theoretically investigated. The pile is assumed to be vertical and elastic, the soil is considered as a linear visco-elastic layer with hysteretic type damping. The layer alone is solved first and the wave modes of the layer are used in the analysis of the pile response. The pile response to a harmonic load is obtained in a closed form and used to define stiffness and damping at the level of the pile head. The dimensionless parameters of the problem are identified. A parametric study is conducted to determine the main features of the response and of the equivalent stiffness and damping. The validity of equivalent viscous damping is examined. A comparison is made with the simpler plane strain theory used previously and its accuracy is assessed.  相似文献   

Dynamic response of single piles embedded in transversely isotropic layered media     

Weiming Liu  Milos Novak 《地震工程与结构动力学》1994,23(11):1239-1257

Dynamic response of single piles embedded in transversely isotropic layered media is investigated using the finite element method combined with dynamic stiffness matrices of the soil derived from Green's functions for ring loads. The influence of soil anisotropy on the dynamic behaviour of piles is examined through a series of parametric studies.  相似文献   

Application of a mixed-layer model to bare soil surfaces     

Michael D. Novak 《Boundary-Layer Meteorology》1991,56(1-2):141-161

A model that couples the surface energy balance equation, a surface hydraulic resistance equation, and the force-restore soil temperature model to a mixed-layer model of the planetary boundary layer is described. The mixed layer is separated from the soil by a relatively thin surface layer and is overlain by a stable free atmosphere with prescribed profiles of potential temperature and water vapour density. The model is in reasonably good agreement with daytime micrometeorological measurements made at a wet bare site at Agassiz, British Columbia, and a desert site at Pampa de La Joya, Peru. The sensitivity of the mixed-layer model to conditions in the free atmosphere, to the parameters describing the growth of the mixed layer, and to surface roughness lengths, surface hydraulic resistance, and windspeed is examined.  相似文献