Diameter Fluctuations Research Articles

1/f noise in nanowires

We have measured the low-frequency resistance fluctuations(1 mHz<f<10 Hz) in Ag nanowiresof diameter 15 nm ≤d≤200 nm at room temperature. The power spectral density (PSD) of the fluctuations has a1/fα character as seen in metallic films and wires of larger dimension. Additionally,the PSD has a significant low-frequency component and the value ofα increases from the usual 1 to as the diameter d is reduced. The value of the normalized fluctuation also increases as the diameter d is reduced. We observe that there are new features in the1/f noise as the size of the wire is reduced and they become more prominent as the diameter of thewires approaches 15 nm. It is important to investigate the origin of the new behaviour as1/f noise may become a limiting factor in the use of metal wires of nanometre dimensions asinterconnects.

Improving water-use efficiency of young lemon trees by shading with aluminised-plastic nets

The experiment was carried out in a research field near Murcia, Spain, over a 3-week period between August 29 and September 17, 2001. Measurements obtained by the continuous monitoring of sap flow and parameters derived from trunk diameter fluctuations were compared with discrete measurements of conventional plant–water status indicators in potted young lemon trees ( Citrus limon (l.) Burm. Fil, cv. Verna) grafted on sour orange ( Citrus aurantium L.) rootstock. Eight trees were used in the experiment, four of which were placed under a rectangular shading net, while the other four were maintained in the open air. The decrease of sap flow in shaded trees with respect to the exposed trees was evident every day. The net also affected trunk diameter changes, with the shaded trees showing lower values of maximum daily shrinkage. High radiation reduced the leaf water potential. In the early morning, the shaded plants opened their stomata later than the plants growing in the open air, and so the transpiration in the latter was higher than in the former during the first hours of the day. However, the net photosynthesis rate was not increased in the exposed plants during these hours of the morning. In the central hours of the day, the leaf stomatal conductance values of exposed plants were lower, as were their instantaneous photosynthesis rates, than the corresponding values in the shaded trees. As a result of the photosynthesis/transpiration balance, it was observed that the best integrated daily water-use efficiency corresponded to the shaded treatment.

Stem and leaf water potentials, gas exchange, sap flow, and trunk diameter fluctuations for detecting water stress in lemon trees

The sensitivity of continuous (on a whole-day basis) and discretely (at midday) measured indicators of the plant water status in adult lemon trees in response to a cycle of water deprivation and recovery, and the feasibility of obtaining baselines for tree water status indicators was investigated in 30-year-old Fino lemon trees (Citrus limon (L.) Burm. fil.) grafted on sour orange (C. aurantium L.) rootstocks. Control plants (T0) were irrigated daily above their crop water requirements in order to obtain non-limiting soil water conditions, while T1 plants were subjected to water stress by withholding irrigation for 50 days, after which time irrigation was restored and plant recovery was studied for 16 days. In T0 plants the water relations and the plant symptoms confirmed that they had not suffered waterlogging. In contrast, T1 plants showed a substantial degree of water stress, which developed very slowly. Maximum daily trunk shrinkage (MDS) increased in response to water stress during the first 15 days of the experiment, but when the stem water potential (Ψstem) fell below −1.8 MPa, the MDS signal intensity decreased. However, Ψstem and sap flow (SF) signal intensities progressively increased during the water stress period. The results showed that MDS is a very suitable plant-based indicator for precise irrigation scheduling in adult lemon trees. Reference or baseline relationships for MDS, Ψstem, and SF measurements as a function of several parameters related to the evaporative demand of the atmosphere were obtained. This fact open up the possibility of considering a plant-based indicator measurement at a given time relative to the expected value under non-limiting water conditions, which can be calculated from the reference relationships.

Prevalence of graft vessel disease after paediatric heart transplantation: a single centre study of 54 patients

The study tested the prevalence of graft vessel disease (GVD) in 54 paediatric heart transplant (HTx) patients (32 male, age 0-17 years) who underwent coronary angiographic investigations (N=117). These were evaluated according to the Stanford classification and additional criteria (peripheral obliterations, diameter fluctuations, pathologic tapering) were applied for risk assessment (no GVD/minimal lesions, GVD without Stanford lesions, accelerated GVD). In H&E stainings from right ventricular endomyocardial biopsies (EMB=169) diagnosis of acute cellular rejection (ACR, ISHLT) and microvasculopathy were performed. Mild rejection was found in 43% (N=44) and severe rejection in 7% (N=7) of EMB early (1st year) and mild rejection in 31% (N=32) and severe in 8% (N=9) late (>3 years) after HTx. Microvasculopathy was present in 22% of EMB. Risk assessment of coronary angiographies showed no GVD/minimal disease in 25% (N=29), GVD without Stanford lesions in 12% (N=14) and different grades of accelerated GVD in 74% (N=74) of studies. All patients dying due to cardiac related causes of death (N=6, 3-12 years after HTx) had evidence of GVD. The data show GVD to be an important cause of late cardiac related deaths in this population.

Neural activity of the cardiac baroreflex decreases with age in normotensive and hypertensive subjects

Baroreflex control of the heart rate is impaired in hypertensive subjects and decreases with age. The decrease in cardiac baroreflex sensitivity (BRS) is often ascribed to decreased distension of the pressure-sensing arterial wall segments. However, alterations in the sensing and processing of neural signals may be involved as well. Conventionally, both vessel wall stiffness and the sensing and neural processing of the baroreflex are incorporated in the measure of pressure-derived BRS. We introduce stretch-derived BRS, which only considers the sensing and neural components of the baroreflex. To determine stretch-derived BRS in a non-invasive manner, we measured the spontaneously occurring low-frequency variations (range, 0.06-0.12 Hz) in the carotid artery diameter and the corresponding R-R interval fluctuations, and determined the associated transfer function. The stretch-derived BRS in a group of age-matched (age range, 25-72 years) normotensive (n = 20) and hypertensive (n = 21) subjects was compared. In both subject groups the stretch-derived BRS decreased significantly with age. Moreover, the stretch-derived BRS of both groups was only different below 50 years of age. The analysis of low-frequency fluctuations in the carotid artery diameter demonstrates that aging as well as hypertension are associated with impaired neural control of the baroreflex. Beyond 50 years of age the effect of hypertension cannot be distinguished from the effect of aging.

Comparison of changes in stem diameter and water potential values for detecting water stress in young almond trees

Trunk diameter fluctuations (TDF) and the leaf water relation parameters, predawn and midday leaf water potential ( Ψ pd and Ψ md), midday stem water potential ( Ψ st) and midday leaf conductance ( g l) were compared for use in detecting water stress and for helping with irrigation management in young almond trees. TDF were monitored throughout 2002 in three irrigation treatments: T 1 (control), irrigated at 120% of crop evapotranspiration (ETc), T 2, at 60% ETc for the whole year and T 3, irrigated at 100% ETc except between 3 June and 15 September, when 40% ETc was supplied. The annual reference crop evapotranspiration and rainfall during the experiment were 1375 and 320 mm, respectively, while the amount of water applied in the treatments was 3165, 1525 and 1430 m 3 ha −1 year −1 for T 1, T 2 and T 3. These irrigation treatments had Ψ st that varied over the season from around −0.65 to −1.0; −0.9 to −1.3 and −0.7 to −1.5 MPa, respectively. Two parameters were obtained from the TDF measurements: (i) maximum daily trunk shrinkage (MDS) and (ii) trunk growth rate (TGR). The MDS values were influenced by the evaporative demand and varied greatly between trees (CV around 10–35%). Although all the water status indicators showed a response to the water supply, the greatest changes were observed in Ψ pd, Ψ st and TGR. The results obtained indicate that MDS and TGR were sensitive to water stress and that TGR is the most useful parameter for quantifying water deficit intensity and duration, its behaviour being very similar to that of Ψ pd and Ψ st. It is concluded that TGR is useful as an indicator of stress and could serve for making irrigation decisions in young almond trees.

Transport and deposition of pyroclastic material from the ∼1000 A.D. caldera-forming eruption of Volcán Ceboruco, Nayarit, Mexico

The complex eruption sequence from the ∼1000 A.D. caldera-forming eruption of Volcan Ceboruco, known as the Jala Pumice, offers an exceptional opportunity to examine how pyroclastic material is transported and deposited from pyroclastic density currents over variable topography. Three main pyroclastic surge deposits (S1, S2, and S3) and two pyroclastic flow deposits (Marquesado and North-Flank PFDs) were emplaced during this eruption. Pyroclastic surge deposits are massive, planar, or cross-bedded, poor-to-well sorted, and display fluctuations in thickness, median diameter, sorting, and lithology as a function of distance, topography, and flow dynamics. Marquesado pyroclastic flow deposits reveal lateral variations from massive, poorly sorted deposits located within 5 km of Ceboruco to planar bedded, moderately well sorted deposits located >15 km away over the nearly horizontal topography to the south of Ceboruco. North-Flank pyroclastic flow deposits also reveal lateral variations from massive, poorly sorted deposits located within 4 km of Ceboruco to planar bedded, moderately well sorted deposits located 8 km away atop an escarpment that steeply rises 230 m from the northern valley floor. Field observations, granulometric analyses, component analyses, and crystal sedimentation calculations along flow-parallel sampling transects all suggest that both surges and flows were density stratified currents, where deposition occurred from a basal region of higher particle concentration that was supplied from an overlying dilute layer that transports particles in suspension. This supports the idea of a transition between “flow” and “surge” end members with variations in particle concentration. Topography greatly affects the transport and depositional capacity of the pyroclastic density currents as a result of “blocking”, either by topographic obstacles or by abrupt breaks at the base of volcano slopes, whereas the origin of Jala Pumice surge deposits (phreatomagmatic versus magmatic) appears to have little impact on their flow dynamics.

Grand Potential, Helmholtz Free Energy, and Entropy Calculation in Heterogeneous Cylindrical Pores by the Grand Canonical Monte Carlo Simulation Method

The adsorption of fluids in porous media is still an open area of research, since no model is able to explain all experimental features. The difficulties rise from the complexity of the real porous materials which present surface heterogeneities, large pore size distributions, and complex networks of interconnected pores. In parallel to experimental efforts trying to produce more ordered porous materials, theoreticians try to introduce more disorder in their models, with the help of molecular simulation for instance. This grand canonical Monte Carlo simulation study concentrates on the adsorption of a simple Lennard-Jones fluid in three porous substrates, to compare the effect of purely geometric heterogeneity (spatial deformation of the external potential) as opposed to purely chemical heterogeneity (amplitude variations of the external potential). This separation is unrealistic, since geometric fluctuations of a real pore diameter along its axis generally induce variations in the amplitude of the external potential created by the pore. However it enables one to compare both effects. In this paper, a thermodynamic integration scheme is applied to a complete set of adsorption/desorption isotherms. The grand potential, free energy, and entropy are calculated, which allows one to discuss the features of the phase diagrams. It is shown that a purely geometric deformation (undulation) of the external potential does not affect the thermodynamic characteristics of the confined fluid. On the other hand, amplitude modulation of the external potential (chemical heterogeneity) strongly distorts the phase diagram. This heterogeneity is actually able to stabilize a "bridgelike" phase which corresponds to an accumulation of molecules in the most attractive region of the pore.

High-speed Melt Spinning of Polyethylene terephthalate with Periodic Oscillation of Take-up Velocity

Abstract To investigate the non-steady-state melt spinning behavior, take-up velocity was varied periodically in the high-speed melt spinning process of polyethylene terephthalate and the time-course changes of velocity and diameter of the spin-line were measured simultaneously. A numerical simulation program for the non-steady-state melt spinning process was also developed. In the range of relatively low take-up velocities, experimental results and results of numerical simulation of the non-steady-state melt spinning process showed a fair agreement, in that the amplitude for the variation of the reciprocal of the cross-sectional area and that for the variation of velocity of the spin-line had a linear relation. An increase in the frequency of velocity oscillation led to a less significant variation in the thickness of as-spun fibers. On the other hand, there was a phase shift between the oscillation of take-up velocity and that of the reciprocal of cross-sectional area of the spin-line at the point of take-up. When take-up velocity was increased, starting of the orientation-induced crystallization along with the occurrence of neck-like deformation caused some characteristic behaviors such as significant increases in the amplitudes of velocity and diameter fluctuations at a certain region in the spin-line. Such behaviors could be reproduced in the numerical calculation by incorporating the stress dependent change of solidification temperature. It was also revealed that the orientation-induced crystallization has the effect of stabilizing the spinning system.

Comparison of continuously recorded plant-based water stress indicators for young lemon trees

Continuously recorded plant-based water stress indicators (sap flow and parameters derived from trunk diameter fluctuations) were compared in potted young lemon trees (Citrus limon (L.) Burm. fil, cv. Verna) grafted on sour orange (C. aurantium L.) rootstock submitted to deficit irrigation. Daily maximum (MXTD) and minimum (MNTD) trunk diameters and daily trunk diameter shrinkage (MDS) were directly influenced by the water supply to the trees from the soil. The continuously recorded plant-based water stress indicators presented different degrees of sensitivity when used to estimate the water status of the plants. Sap flow (SF) and MDS were more immediate and sensitive than MXTD and MNTD. However, the higher signal intensity: noise for SF and the fact that its signal intensities remained clearly above unity during the stress period, indicating that the soil water was depleted, point to the greater reliability of this indicator. Also, the possibility of developing further baseline relationships between SF and air vapour pressure deficit in fully irrigated trees in field conditions increases the feasibility of using this parameter in automatic irrigation systems.

ESTABLISHING REFERENCE VALUES OF TRUNK DIAMETER FLUCTUATIONS AND STEM WATER POTENTIAL FOR IRRIGATION SCHEDULING OF OLIVE TREES

Trunk diameter fluctuations (TDF) and stem water potential (SWP) were recorded in well-irrigated olive trees with the aim of establishing reference values of both indicators for irrigation scheduling. The measurements were performed in a mature (18 years) and a young olive orchard (3 years) during 4 years. Two different indicators derived from TDF: maximum daily shrinkage (MDS) and trunk growth rate (TGR) were evaluated. The annual relationship between MDS and vapour pressure deficit (VPD) was hysteretic, probably caused by the presence of fruit as no hysteresis was detected in ‘off’ trees. All data pooled gave an equation of MDS=0.09+0.19VPD (R 2 =0.60). When only data until mid-August in mature “on” trees was used, the fit was improved (R 2 =0.71; MDS=0.05+0.22VPD). Young trees had a slightly different relationship with a steeper slope; MDS=-0.18+0.27VPD (R 2 =0.80). The relationships between the SWP values and VPD were not as good as with MDS (R 2 around 0.3), and the regression slope was steeper in ‘on’ than in ‘off’ trees. TGR in the young orchard had two maxima in the year; the first at mid-Spring (0.2 mm day -1 ) and the second at the end of the summer (0.15 mm day -1 ). In the mature orchard, TGR had a single maximum value, at the end of summer for ‘off’ trees, and in spring for ‘on’ trees.

Epicardial and microvascular graft vessel disease in children

Graft vessel disease (GVD) is one of the main limiting factors to long-term survival after adult heart transplantation (HTx). The incidence of epicardial and microvascular GVD in paediatric patients was studied. A total of 137 coronary angiographies from 130 paediatric HTx and heart and lung transplant (HLTx) patients (70 male, 60 female, aged 0-18 y) were evaluated according to the Stanford classification and its supplements (minor vessel alterations). In H&E stainings from right ventricular endomyocardial biopsies (EMB = 397), light microscopic diagnosis of acute cellular rejection (ISHLT classification) and vascular reaction (morphology of endothelial cells and vessel walls) was performed. Moderate rejection was present in 32.8% and severe rejection in 13.3% of EMB. Microvascular EC swelling was found in 33.5% and vessel wall thickening in 53.8% of EMB. The results of the coronary angiographic investigations were: Stanford lesions = 61.2%, peripheral obliterations = 52.5%, diameter fluctuations = 86.3%, pathologic tapering = 64.0%, calcifications = 10.8%. Long-term survivors (> or =5 y) showed macrovascular alterations in 78% of cases and microvascular alterations in 67% of cases. The development of micro- and macrovascular GVD is one of the predominant complications in long-term survivors after paediatric HTx and HLTx.

Processes preventing nocturnal equilibration between leaf and soil water potential in tropical savanna woody species.

The impact of nocturnal water loss and recharge of stem water storage on predawn disequilibrium between leaf (psiL) and soil (psiS) water potentials was studied in three dominant tropical savanna woody species in central Brazil (Cerrado). Sap flow continued throughout the night during the dry season and contributed from 13 to 28% of total daily transpiration. During the dry season, psiL was substantially less negative in covered transpiring leaves, throughout the day and night, than in exposed leaves. Before dawn, differences in psiL between covered and exposed leaves were about 0.4 MPa. When relationships between sap flow and psiL of exposed leaves were extrapolated to zero flow, the resulting values of psiL (a proxy of weighted mean soil water potential) in two of the species were similar to predawn values of covered leaves. Consistent with substantial nocturnal sap flow, stomatal conductance (gs) never dropped below 40 mmol m(-2) s(-1) at night, and in some cases, rose to as much as 100 mmol m(-2) s(-1) before the end of the dark period. Nocturnal gs decreased linearly with increasing air saturation deficit (D), but there were species-specific differences in the slopes of the relationships between nocturnal gs and D. Withdrawal and recharge of water from stem storage compartments were assessed by monitoring diel fluctuations of stem diameter with electronic dendrometers. Stem water storage compartments tended to recharge faster when nocturnal transpiration was reduced by covering the entire plant. Water potential of covered leaves did not stabilize in any of the plants before the end of the dark period, suggesting that, even in covered plants, water storage tissues were not fully rehydrated by dawn. Patterns of sap flow and expansion and contraction of stems reflected the dynamics of water movement during utilization and recharge of stem water storage tissues. This study showed that nighttime transpiration and recharge of internal water storage contribute to predawn disequilibrium in water potential between leaves and soil in neotropical savanna woody plants.

Sap flow and trunk diameter fluctuations of young lemon trees under water stress and rewatering

Potted 2-year-old lemon trees ( Citrus limon (L.) Burm. fil, cv. Verna) grafted on sour orange ( C. aurantium L.) rootstock and growing under field conditions were subjected to water stress by withholding irrigation for 6 days. After that time, irrigation was restored and plant recovery was studied for 8 days. The results indicate that sap flow (SF) measurement by the heat-pulse technique is a suitable plant-based method for estimating the daily transpiration for young lemon plants. The most sensitive continuously recorded plant-based indicators of water stress and recovery were daily minimum trunk diameter (MNTD) and daily maximum trunk shrinkage (MDS) followed by SF. It was concluded that the water supplied to the trees from soil has a direct influence on daily MDS. Besides reflecting tree water status, SF and MNDT were clearly influenced by weather conditions, meaning that it is possible to develop reference or baseline relationships to interpret plant-based indicator measurements for irrigation scheduling.

Interpreting trunk diameter changes in young lemon trees under deficit irrigation

Measurements obtained by the continuous monitoring of sap flow and parameters derived from trunk diameter fluctuations were compared with discrete measurements of conventional plant water status indicators in potted young lemon trees ( Citrus limon (l.) Burm. fil, cv. Verna) grafted on sour orange ( C. aurantium L.) rootstock submitted to high frequency deficit irrigation. The first detectable response to the deficit irrigation was a marked increase in maximum daily trunk diameter shrinkage (MDS) followed by a decrease in sap flow (SF), predawn leaf water potential and leaf conductance values. Daily maximum (MXTD) and minimum (MNTD) trunk diameters were directly influenced by the plant water supply from the soil. When the water stress increased in severity and the trunk growth rate increased, the MDS values in treated plants decreased to reach values similar to those of control plants. Thus, during the first days of deficit irrigation, when trunk growth was very low, MDS and SF served as the best plant water status indicators. Further, when water stress was more pronounced and trunk growth was greater, MNTD, MXTD and SF were the most reliable indicators.

Deterministic nonlinear characteristics of in vivo blood flow velocity and arteriolar diameter fluctuations

We have performed a nonlinear analysis of fluctuations in red cell velocity and arteriolar calibre in the mesenteric bed of the anaesthetized rat. Measurements were obtained under control conditions and during local superfusion with NG-nitro-L-arginine (L-NNA, 30 µM) and tetrabutylammonium (TBA, 0.1 mM), which suppress NO synthesis and block Ca2+ activated K+ channels (KCa), respectively. Time series were analysed by calculating correlation dimensions and largest Lyapunov exponents. Both statistics were higher for red cell velocity than diameter fluctuations, thereby potentially differentiating between global and local mechanisms that regulate microvascular flow. Evidence for underlying nonlinear structure was provided by analysis of surrogate time series generated from the experimental data following randomization of Fourier phase. Complexity indices characterizing time series under control conditions were in general higher than those derived from data obtained during superfusion with L-NNA and TBA.

Analysis of Defects in Poly(ethylene terephthalate) Fibers

The distribution of tensile strength and the defect sensitivity of a poly(ethylene terephthalate) fiber for industrial use have been investigated. A fiber with low defect sensitivity refers to the fiber having a tough fiber structure against defects. The distribution of strength was brought about by the variation of the defect sensitivity as well as the variation of the severity of defects. The filament had fluctuation in diameter and the thinner portion of the filament showed lower defect sensitivity. The defect size and the strength of the fiber attained by eliminating defects were estimated based on the strength of notched fibers.

An experimental system for analysis of the dynamic sap-flow characteristics in young trees: results of a beech tree.

This paper describes an experimental system designed for analysis of the dynamic water flow through young trees, complemented with test results of a 2-year-old beech tree (Fagus sylvatica L.). The system allows automatic and simultaneous measurements of a complex set of plant physiological processes at leaf, branch, stem and root levels [transpiration (E), sap flow (F) and diameter fluctuations (Δd)], in combination with the micrometeorological variables that control these processes [soil and air temperature (Ts and Ta), vapour pressure deficit of the air (D) and photosynthetically active radiation (PAR)]. A 2-d experimental period was used to study the whole-tree water transport dynamics of the young beech tree. Good correspondence between E of the leaves and F in the supporting branch was found. An increased time lag between the F measurements along the hydraulic pathway down towards the root system was observed, indicating the non-steady-state nature of the water flow. The daytime Δd of stem and branch revealed the depletion and the replenishment of internal water reserves. The daily amount of water withdrawn from internal storage was 5% of the total daily transpiration. A good linear relationship was found between the rate of change in internal water storage and the rate of change in stem diameter, having no time lag. We conclude that the data obtained with this system will allow experimental assessment of hydraulic properties in young trees and facilitate calibration of models for non-steady-state conditions of water flow in young trees.

Complex Diameter Modulations in Silicon Carbide Nanowire Growth

ABSTRACTSilicon carbide nanowires were grown via a self-organized process. Some of the nanowires showed complex diameter fluctuations. The fluctuation was studied from the viewpoints of random walk and fractal. Power spectrum analysis of a fluctuation revealed that the fluctuation was not periodic and that the spectrum was colored. The distribution of increments had a fat tail which was not Gaussian but obeyed power law. Thus the diameter fluctuation was interpreted as a Lévy Flight. In addition, the fluctuation also showed multiaffine scaling.

Growth assessment in tropical trees: large daily diameter fluctuations and their concealment by dendrometer bands

Tree stems contract and expand as stem water is depleted and replaced. Band-dendrometer studies suggest that such daily changes are small (&lt;0.2 mm diameter), and they are ignored in most growth measurements. However, several studies using other approaches note larger changes (even &gt;1 cm diameter), suggesting that significant biases are possible. An exploratory study examined the pattern and magnitude of daily stem changes and whether commercial band-dendrometers were able to reveal them. A method involving multiple precision measurements on eight trees in a Bornean hill dipterocarp forest revealed daily shrinkage and expansion of girth of around 1 mm. Fluctuations were greater in bright weather. Band-dendrometers detected these changes but revealed less than a tenth of their magnitude. An analytical model for dendrometer error is presented that predicts how measurement biases can be reduced. Tropical trees can fluctuate appreciably in stem diameter over the day. These reversible changes are of sufficient magnitude to merit concern in growth studies. Influential biases seem especially likely when measurement intervals are short and involve systematic differences in timing and weather. Further study is required to gauge the more general influence of these measurement problems.