Vertical Spacers Research Articles

Combined effects of vertical spacers and segregation on mass transport properties of reinforced concrete

All concrete structures contain reinforcement spacers, and deep sections can be affected by bleeding and segregation without displaying visible indications during casting. However, their effects on mass transport and long-term durability are not well studied. In this paper, reinforced concrete columns were prepared with plastic and cementitious spacers to achieve 50 mm cover, and compacted at different vibration frequencies and durations. 28d cured samples were extracted along the height, conditioned to equilibrium (21 °C, 75% RH or 50 °C, 7% RH), and then subjected to water absorption, electrical conduction, epoxy impregnation and fluorescence imaging. Samples from the top of the column consistently gave higher accessible porosity and mass transport compared to samples from the bottom. Presence of spacers caused additional increases in mass transport because of preferential flow through the spacer-concrete interface which is more porous and microcracked compared to bulk concrete farther away. Image analysis on cross-sections showed that the columns experienced some aggregate segregation despite care taken to avoid over-compaction. The resistance of concrete to ingress of aggressive agents decreases with increasing height due to the combined negative effects of reinforcement spacers and segregation.

ChemInform Abstract: Supramolecular Explorations: Exhibiting the Extent of Extended Cationic Cyclophanes

AbstractReview: 61 refs.

(Invited) Record-Performance In(Ga)As MOSFETS Targeting ITRS High-Performance and Low-Power Logic

We review recent development of In(Ga)As-channel MOSFETs. Low-effective mass InAs and InGaAs channels, combined with thin gate dielectrics, provide high transconductance, but off-state leakage can be high due to band-band and source-drain tunneling currents. This leakage is reduced through thin 2.5-3nm channels, and through InGaAs or wide-bandgap InP vertical field spacers in the raised, regrown source and drain. Planar UTB devices with 2.7nm thick strained InAs channels and lightly-doped InGaAs spacers in the raised regrown source and drain provide, at 25nm gate length, record 0.5mA/µm on-current at 100nA/µm off-current (ITRS HP specification) and 500mV VDD. 1 µm gate length FETs show 61mV/decade subthreshold swing at 0.1 Volts VDD. Targeting the ITRS LP specification, we have developed InGaAs-channel MOSFETs with lightly-doped InP wide-bandgap spacer layers in the raised source and drain. At 30nm gate length, these show a minimum 60 pA/µm off-current, approximately 100:1 smaller than a similar device using InGaAs source/drain spacers. A FET using InP spacers, with 45 nm gate length, shows 0.15 mA/µm on-current at 1nA/µm off-current (ITRS GP specification) and 500mV VDD. We will discuss ongoing efforts to further increased on-current and decrease off-current in short-gate-length III-V MOSFETs.

(Invited) Record-Performance In(Ga)As MOSFETS Targeting ITRS High-Performance and Low-Power Logic

We review development of In(Ga)As-channel MOSFETs. InAs and InGaAs channels, combined with thin gate dielectrics, provide high transconductance, but off-state leakage can be high due to band-band tunneling currents. This leakage is reduced through thin 2.5-3nm channels, and through InGaAs or InP vertical field spacers in the raised source and drain. Devices with 2.7nm InAs channels and lightly-doped InGaAs source/drain spacers, at 25nm Lg , provide a record 0.5mA/µm Ion at 100nA/µm Ioff and 500mV VDD . 1 µm Lg FETs show 61mV/decade subthreshold swing at VDD =0.1 V. Targeting the LP specification, we have developed InGaAs-channel MOSFETs with lightly-doped InP wide-bandgap source/drain spacer layers. At 30nm gate length, these show a minimum 60 pA/µm Ioff , approximately 100:1 smaller than a similar device using InGaAs source/drain spacers. A FET using InP spacers, with 45 nm gate length, shows 0.15 mA/µm Ion at 1nA/µm Ioff and 500mV VDD .

Development of a Three Dimensional Neural Sensing Device by a Stacking Method

This study reports a new stacking method for assembling a 3-D microprobe array. To date, 3-D array structures have usually been assembled with vertical spacers, snap fasteners and a supporting platform. Such methods have achieved 3-D structures but suffer from complex assembly steps, vertical interconnection for 3-D signal transmission, low structure strength and large implantable opening. By applying the proposed stacking method, the previous techniques could be replaced by 2-D wire bonding. In this way, supporting platforms with slots and vertical spacers were no longer needed. Furthermore, ASIC chips can be substituted for the spacers in the stacked arrays to achieve system integration, design flexibility and volume usage efficiency. To avoid overflow of the adhesive fluid during assembly, an anti-overflow design which made use of capillary action force was applied in the stacking method as well. Moreover, presented stacking procedure consumes only 35 minutes in average for a 4 × 4 3-D microprobe array without requiring other specially made assembly tools. To summarize, the advantages of the proposed stacking method for 3-D array assembly include simplified assembly process, high structure strength, smaller opening area and integration ability with active circuits. This stacking assembly technique allows an alternative method to create 3-D structures from planar components.

Label-free detection of DNA mutations by SPR: application to the early detection of inherited breast cancer

A screening analysis of DNA hybridization and the presence of DNA mutations using an surface plasmon resonance (SPR) biosensor is shown. The influence of lateral and vertical spacers, as well as several hybridization conditions, was studied to optimize the differentiation between fully complementary and mismatched DNA strands. Our results demonstrated that SPR biosensors were able to detect mismatch sequences related to inherited breast cancer, with high specificity and sensitivity. Using PCR synthetic sequences as targets, mutant sequences were clearly discriminated from fully complementary ones, and detection limits below 50 nM were achieved.

The Role of Leaf Lobation in Elongation Responses to Shade in the Rosette-forming Forb Serratula tinctoria (Asteraceae)

Lobed leaves are considered selectively advantageous in conditions of high irradiance. However, most studies have involved woody species, with only a few considering the role of leaf lobation in herbaceous rosette species. In this study, it is hypothesized that, in addition to its adaptive value in high light, leaf lobation may add to the function of petioles as vertical spacers in herbaceous species in conditions of strong competition for light. To test this hypothesis, leaf development was examined under seasonally changing natural light conditions and a field experiment was conducted in which light climate was manipulated in a wooded meadow population of Serratula tinctoria. No changes in leaf lobation were observed in response to experimental shading or different natural light conditions. However, in tall herbaceous vegetation, plants with highly lobed leaves achieved significantly greater vertical elongation than plants with less-lobed leaves. In contrast to herbaceous shade, tree shade had no effect on leaf elongation, suggesting differential responsiveness to competition from neighbouring herbs versus overhead shade. In shading treatments, imposed shade could only be responded to by the elongation of leaves that were produced late in development. The results show that extensive leaf lobation can enable greater leaf elongation in response to shade from surrounding herbaceous vegetation. The different morphological responses displayed by Serratula tinctoria to different types of shade demonstrate the importance of critically assessing experimental designs when investigating phenotypic plasticity in response to shade.

Lack of Differential Plasticity to Shading of Internodes and Petioles with Growth Habit inConvolvulus arvensis(Convolvulaceae)

It has been postulated that the plasticity to shading of spacing organs in plants of different growth habit is more likely related to the analogy of organs than to their homology. Accordingly, vertical spacers (internodes in erect species, petioles in prostrate species) should be more plastic than horizontal spacers (petioles in erect species, internodes in prostrate species). This hypothesis was tested in the climbing plant Convolvulus arvensis. Given their facultative erect or prostrate habit, depending on support availability, climbing plants may be model species to test the relationship between growth habit and spacer plasticity in the absence of the confounding factors that are typical of interspecific comparisons. The phenotypic correlations among traits were also addressed. Three shading treatments (100%, 20%, and 5% of sunlight) and two support conditions (with and without a stake on which plants could twine) provided the experimental setting. Traits evaluated included internode length, petiole length, stem thickness, and biomass as well as area, shape, and specific area of leaves. The hypothesis was not supported. Internodes were more plastic than petioles in supported (“erect”) as well as in nonsupported (“prostrate”) plants, thereby supporting homology, and not analogy, of organs as a factor in explaining plasticity patterns. Most traits were significantly correlated both in supported and nonsupported plants. Internode and petiole length showed a highly significant positive correlation. This is discussed, and trait correlations are considered as possible constraints on the expected pattern of differential spacer plasticity to shading.

A Comparative Study of Spacer Plasticity in Erect and Stoloniferous Herbs

Closely related plant species from a number of genera produce either erect (orthotropic) or creeping (plagiotropic) shoots. As a result, corresponding (homologous) organs, such as internodes or petioles, are oriented differently in space. They thus fulfil different functions; the elongation of vertically oriented structures shifts leaf blades into higher regions within the canopy, whereas the elongation of horizontally oriented structures does not. As a consequence, different degrees of internode or petiole plasticity may have evolved in erect and stoloniferous species to adjust the architecture of plants in case they are shaded. This study aims at testing the hypothesis that vertically oriented spacers have higher degrees of shade-induced plasticity in their length than horizontally oriented spacers. It is further hypothesized that a high degree of plasticity in spacer length involves costs in terms of increased biomass investment into elongating organs. These hypotheses were tested with nine herbaceous species pairs (each consisting of one erect and one closely related stoloniferous species) belonging to six different families of dicots. Vertical spacers had higher degrees of shade-induced plasticity than horizontal spacers. This was true for internodes and petioles of individual species and also for functionally corresponding (i.e. analogous) spacers within species pairs. In addition, plastic increases in spacer length were positively related to increased spacer weight and to increased biomass allocation to spacers under shaded conditions. These results show that spacer plasticity depends primarily on the function of spacers and not on the phylogenetic relations of the species. They also suggest that there are costs of plasticity in terms of biomass investment into elongating organs. Differences in the balance between costs and benefits of plasticity between vertical and horizontal spacers may have led to the evolution of high degrees of plasticity of vertically oriented spacers and low degrees of plasticity of horizontally oriented spacers, as observed in this study.

Differential response to shading in orthotropic and plagiotropic shoots of the clonal herb Glechoma hirsuta.

Previous studies have shown that internodes and petioles of closely related erect and stoloniferous species show marked differences in their response to shading. Vertical structures show strong elongation responses while horizontal structures show significantly smaller elongation responses. This paper reports an experiment designed to test whether internodes and petioles on orthotropic (vertically oriented) and plagiotropic (horizontally oriented) shoots produced by the same plant, also show such differential responses. The study species, Glechoma hirsuta, produces plagiotropic shoots in its vegetative stage and orthotropic shoots during its generative stage. Shoots of G. hirsuta were grown either in full daylight or under simulated canopy shade. Internode and petiole elongation, biomass investment patterns and other growth-related parameters were measured on plants in each light treatment. In orthotropic shoots the length of internodes responded more strongly to shading than the length of petioles, while the opposite was true for plagiotropic shoots, confirming the hypothesis that vertical spacers have higher degrees of shade-induced plasticity than horizontally oriented spacers. Growth and development of horizontally oriented shoots was reduced by shading, whereas that of vertically oriented shoots was unaffected by light treatment. The results are discussed in terms of the differences in function of vertically and horizontally oriented spacers, and the probable benefits of plasticity in enhancing essential activities including photosynthesis, habitat exploration and seed dispersal.

Plasticity of Internodes and Petioles in Postrate and Erect Potentilla Species

1. In phylogenetically related species, internodes of erect and stoloniferous plants are homologous structures, whereas petioles of prostrate plants and internodes of erect plants are structurally analogous, i.e. they have the same ecological function. 2. The hypothesis was tested that analogous spacing organs would show similar degrees of plasticity in response to shading, whereas homologous spacing organs would not. Four closely related Potentilla species representing a range of growth forms from strictly erect to obligatory stoloniferous were studied. 3. Vertical spacers showed significantly higher degrees of plasticity than horizontal spacers in response to shading, confirming the hypothesis that analogous organs show a similar response, whereas homologous spacers differed significantly in their plasticity. 4. Under shaded conditions high degrees of elongation in vertical spacers were accompanied by a significant increase in biomass allocation to these organs, whereas allocation to horizontal spacers tended to be less than under unshaded conditions. This result suggests that significant biomass investments are associated with plastic elongation responses. 5. The results of the study are discussed in the context of specific selection pressures acting on different growth forms which may alter the degree of morphological plasticity of plant organs during evolution.

Exact solutions for elastic cable systems

Analytical solutions are derived for the static response of two elastic cable systems under the action of distributed and concentrated vertical loadings. The first system is a general cable truss with an arbitrary number of vertical spacers, the second a highly symmetric 2 × 2 cable network. The analysis of both features a pair of lagrangian coordinates, one associated with the strained profile and the.other with the unstrained profile. Cable tensions and positions in the strained state are represented as functions of the latter. A specific application of these functions is made for each system.

Effect of Tension Changes on Cable Truss Stability

Recently, a theory has been presented for the lateral stability of certain simple forms of the cable truss. The term cable truss is taken to mean a structural member consisting of prestressed cables, commonly of opposite curvature, that form the chords of the truss and, between which, vertical spacers are placed to define initial profile geometry and to provide for the transfer of load between the chords. Cable trusses have been used in arrays to support the roofs of large-span buildings.

Effects of horizontal and vertical spacers on the heat transfer across a horizontal, annular, air-filled cavity

Flow patterns and temperature profiles, as well as local and overall heat transfer coefficients, were measured for a horizontal, annular cavity, containing air at atmospheric pressure. The radius ratio of the bounding surfaces of the cavity was 1·5, the inner cylinder being heated. The insertion of two horizontal, radial, co-planar spacers bridging the 18·9 mm cavity along its whole length, reduced the convective rate of heat transfer from the surface of the inner cylinder whereas the same co-planar spacers, if vertical, led to an increased rate of convective heat transfer. Flow instabilities, encountered in the plain cavity, were also eliminated by the insertion of the horizontal spacers.