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In this article, we describe the results of the second phase of a randomized controlled trial of Minding the Baby (MTB), an interdisciplinary reflective parenting intervention for infants and their families. Young first-time mothers living in underserved, poor, urban communities received intensive home visiting services from a nurse and social worker team for 27 months, from pregnancy to the child's second birthday. Results indicate that MTB mothers' levels of reflective functioning was more likely to increase over the course of the intervention than were those of control group mothers. Likewise, infants in the MTB group were significantly more likely to be securely attached, and significantly less likely to be disorganized, than infants in the control group. We discuss our findings in terms of their contribution to understanding the impacts and import of intensive intervention with vulnerable families during the earliest stages of parenthood in preventing the intergenerational transmission of disrupted relationships and insecure attachment.
Formal grammars such as L-systems have long been used to describe plant growth dynamics. In this article, they are used for a new purpose. The aim is to build a symbolic method that enables the computation of the stochastic distribution associated with the number of complex structures in plants whose organogenesis is driven by a multitype branching process. For that purpose, a new combinatorial framework is set in which plant structure is coded by a Dyck word. Moreover, organogenesis is represented by stochastic F0L-systems. In doing so, the problem is equivalent to determining the distribution of patterns in random words generated by a stochastic F0L-system. This method finds interesting applications in the parameter identification of stochastic models of plant development.
In this paper we introduce a novel, flexible, system for mechanical deformation detection. The core of the system is based on an Organic Thin Film Transistor (OTFT) which has been assembled on a flexible PET substrate and patterned by means of inkjet printing. OTFT-based mechanical sensors were fabricated employing two different organic semiconductors, namely a small molecule (pentacene) deposited by thermal evaporation and its solution-processable derivative 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) deposited by drop casting. It will be shown that the surface deformation induced by an external mechanical stimulus gives rise in both cases to a marked, reproducible and reversible (within a certain rage of surface deformation) variation of the device output current. Starting from these results, more complex structures such as arrays and matrices of OTFT-based mechanical sensors have been fabricated by means of inkjet printing. Thanks to the flexibility of the introduced structure, we will show that the presented system can be transferred on different surfaces (hard and soft) and employed for a wide range of applications. In particular, we have designed and fabricated a fully functional system based on a matrix of 64 elements that can be employed for detecting mechanical stimuli over larger areas, and will demonstrate that such a system can be successfully employed for tactile transduction in the realization of artificial “robot skins”.
A survey of the Maine landscape and nursery industry was conducted to identify industry views on invasive plant issues, attitudes towards potential regulation, and to estimate the potential economic costs of banning the sale of specific invasive plant species in Maine. Analysis of the 190 surveys returned (19% of 980 mailed) revealed that 76% of industry member respondents were genuinely concerned about invasive plant issues, and the same percentage felt the horticulture industry is responsible for educating customers about invasive plants. Industry members (68%) did not feel compelled to sell invasive plants merely on the basis of customer attraction to the plant, or due to competition with a neighboring business that sells the invasive plant. Self-reporting of sales indicated that Norway maple ($96K), burningbush ($68K), and Japanese barberry ($44K) constituted the largest portion of annual industry revenue (maximum values reported for 2006 to 2008) derived from the sale of seven identified invasive plants. Industry self-regulation was the most favored form of regulation, although the industry likely would not be significantly affected by legislated state-wide bans of at least purple loosestrife and oriental bittersweet. Bans on other popular invasive plants, including burningbush, Japanese barberry, and Norway maple likely would have a relatively small, short-term impact on the horticulture industry until alternative plants with similar properties were identified. The results of this survey demonstrated a need for identifying which plants are truly invasive or potentially invasive in Maine, as well as a need for open discussion of invasive plant issues among all interested parties in Maine.
The cw absorption, steady state photoluminescence (PL), photoinduced absorption (PA), PL-detected magnetic resonance (PLDMR), and the time resolved PL of a novel polyfluorene (PF) prepared with bulky polyphenylene dendrimer substituents are compared with those of (PF) with ethyl-hexyl substituents. We show that the dendronic sidechains suppress the contribution from unwanted low energetic emission, yielding a polymer with pure blue emission. The sidechains also strongly alter the dynamics of the excited entities. In particular, the time-resolved PL and temperature-dependence of the cw PL from 20-320 K reveal distinct singlet exciton (SE) dynamics in the polymer films, while the behavior in solution is essentially the same. However, the PA results show that the dynamics of polarons and triplet excitons (TEs) are similar, and the PLDMR shows that the interaction between the SEs and polarons are also similar.
Aerogels were structurally modified using chemical vapor deposition (CVD) of cyanoacrylate monomers to afford polycyanoacrylate-aerogel nanocomposites. Silica aerogels are low density, high surface area materials whose applications are limited by their fragility. Cyanoacrylate CVD allowed us to deposit a film of organic polymer throughout fragile porous monoliths within hours. Our experiments have shown that polymerization of the cyanoacrylate monomers was initiated by the adsorbed water on the surface of the silica permitting the nanocomposites structures to be formed with little or no sample preparation. We found that the strength of the polycyanoacrylate-aerogel nanocomposites increased thirty two-fold over the untreated aerogels with only a three-fold increase in density and an eight-fold decrease in surface area. Along with the improvement in mechanical properties, the aerogels became less hydrophilic than un-modified aerogels. Polycyanoacrylate-coated aerogels were placed directly into water and did not suffer catastrophic fragmentation as observed with un-modified silica aerogels.
By definition, half of all interconnects fail before the measured mean time to failure (t50) is reached. To predict early failures the basic reactions occurring in the metallization and its environment must be understood. To this end, fatal interconnect failure sites were characterized by Auger electron spectroscopy, atomic force microscopy and backscattered scanning electron microscopy. CVD silicon dioxide passivation layer/fatal void interfaces of typical early failure voids were characterized and compared to a typical late failure void interface. The topographies of these fatal voids were also quantitatively compared to increase our understanding of early failure sites and electromigration.
Arylene- and alkylene-bridged polysilsesquioxanes were prepared by sol-gel
processing of bis(triethoxysilyl)-arylene monomers 1-4, and alkylene
monomers 5-9. The arylene polysilsesquioxanes were porous materials with
surface areas as high as 830 m2/g (BET). Treatment with an
inductively coupled oxygen plasma resulted in the near quantitative removal
of the arylene bridging groups and a coarsening of the pore structure. Solid
state 29Si NMR was used to confirm the conversion of the
sesquioxane silicons (T) to silica (Q). The alkylene-bridged
polysilsesquioxanes were non-porous. Oxygen plasma treatment afforded silica
gels with mesoporosity. The porosity in the silica gels appears to arise
entirely from the oxidation of the alkylene spacers.
Hexylene-and phenylene-bridged polymethylsiloxane xerogels X-2 and X-4,
respectively, were prepared by the sol-gel hydrolysis and condensation of 1,
6-bis(diethoxymethyl-silyl)hexane 1 and 1, 4-bis(diethoxymethysilyl)benzene
2 under acidic and basic conditions. These polymerizations afforded network
polymers in the form of wet gels within several hours. The gels were
processed to afford xerogels whose characteristics (determined by solid
state 13C and 29Si CP MAS NMR spectroscopy and
nitrogen sorption porosimetry) were compared and contrasted with those of
their analogous polysilsesquioxanes. 29Si CP MAS NMR indicates a
high, degree of hydrolysis and polycondensation; porosimetry measurements
reveal that the materials have significant surface areas, save for the
acid-catalyzed hexylene gels X-2.
Under acidic sol-gel polymerization conditions, 1,3-bis(triethoxysilyl)-propane 1 and 1,4-bis(triethoxysilyl)butane 2 were shown to preferentially form cyclic disilsesquioxanes 3 and 4 rather than the expected 1,3-propylene- and 1,4-butylene-bridged polysilsesquioxane gels. Formation of 3 and 4 is driven by a combination of an intramolecular cyclization to six and seven membered rings, and a pronounced reduction in reactivity under acidic conditions as a function of increasing degree of condensation. The ease with which these relatively unreactive cyclic monomers and dimers are formed (under acidic conditions) helps to explain the difficulties in forming gels from 1 and 2. The stability of cyclic disilsesquioxanes was confirmed with the synthesis of 3 and 4 in gram quantities; the cyclic disilsesquioxanes react slowly to give tricyclic dimers containing a thermodynamically stable eight membered siloxane ring. Continued reactions were shown to perserve the cyclic structure, opening up the possiblity of utilizing cyclic disilsesquioxanes as sol-gel monomers. Preliminary polymerization studies with these new, carbohydrate-like monomers revealed the formation of network poly(cyclic disilsesquioxanes) under acidic conditions and polymerization with ring-opening under basic conditions.
The spectral editing properties of the 29Si NMR INEPT heteronuclear transfer experiment have been utilized for the identification and characterization of hydrolysis and initial condensation products in methyltrimethoxysilane (MTMS) sol-gel materials. 29Si NMR assignments in MTMS are complicated by a small spectral dispersion (∼0.5 ppm) and two different 29Si-1H J couplings. By using analytical expressions for the INEPT signal response with multiple heteronuclear J couplings, unambiguous spectral assignments can be made. For this organomethoxysilane the rate of hydrolysis was found to be very rapid and significantly faster than either the water- or alcohol-producing condensation reactions. The hydrolysis species of both the MTMS monomer and its initial T1 condensation products follow statistical distributions that can be directly related to the extent of the hydrolysis reactions. The role of the statistical distribution of hydrolysis products on the production and synthetic control of organically modified sol-gels is discussed.
The retro Diels-Alder reaction was used to modify porosity in hydrocarbon-bridged polysilsesquioxane gels. Microporous polysilsesquioxanes incorporating a thermally labile Diels-Alder adduct as the hydrocarbon bridging group were prepared by sol-gel polymerization of trans-2, 3-bis(triethoxysilyl)norbornene. Upon heating the 2, 3-norbornenylene-bridged polymers at temperatures above 250°C, the norbornenylene-bridging group underwent a retro Diels-Alder reaction losing cyclopentadiene and leaving behind a ethenylene-bridged polysilsesquioxane. Less than theoretical quantities of cyclopentadiene were volatilized indicating that some of the diene was either reacting with the silanol and olefinic rich material or undergoing oligomerization. Both scanning electron microscopy and nitrogen sorption porosimetry revealed net coarsening of pores (and reduction of surface area) in the materials with thermolysis.
We investigate the porosity of a series of xerogels prepared from arylene-bridged silsesquioxane xerogels as a function of organic bridging group, condensation catalyst and post-synthesis plasma treatment to remove the organic functionalities. We conclude that porosity is controlled by polymer-solvent phase separation in the solution with no evidence of organic-inorganic phase separation. As the polymer grows and crosslinks, it becomes increasingly incompatible with the solvent and eventually microphase separates. The domain structure is controlled by a balance of network elasticity and non-bonding polymer-solvent interactions. The bridging organic groups serve to ameliorate polymer-solvent incompatibility. As a result, when the polymer does eventually phase separate, the rather tightly crosslinked network limits domain size to tens of angstroms, substantially smaller than that observed in xerogels obtained from purely inorganic precursors where incompatibility drives phase separation earlier in the gelation sequence.
Hydrolysis and condensation of trialkoxysilanes, HSi(OMe)3 and HSi(OEt)3, has been used to prepare polyhydridosilsesquioxaes for dielectric applications. In this study we examined the ability of trimethoxysilane (TMS) and triethoxysilane (TES) to undergo sol-gel polymerization to afford gels. Sol-gel polymerization experiments were conducted under acidic (HCl), basic (NaOH), and neutral conditions in methanol or ethanol. Gels prepared with basic catalysts were exothermic with the evolution of hydrogen gas. Gel times are compared with silica gels prepared from tetramethoxysilane (TMOS) and tetraethoxysilane (TEOS). Gels were worked up under aqueous conditions to afford xerogels. Surface area analyses by nitrogen sorption porosimetery revealed that the materials were mostly mesoporous materials with surface areas in the hundreds of square meters per gram. Solid state 29Si CP MAS NMR was used to determine the amount of hydrido group remaining in the xerogels. Gels prepared under acidic conditions were essentially polysilsesquioxanes with very little loss of hydride functionalities. In gels prepared under basic conditions the hydride groups were completely gone leaving silica gels. Gels prepared with neutral water lost approximately 66% of the hydride groups.
The introduction of organic substituents into sol-gel materials can often result in networks that collapse during drying to afford non-porous xerogels. This can prove useful if non-porous coatings or membranes are the ultimate objectives. Collapse of porosity is also manifested in bridged polysilsesquioxanes with flexible bridging groups. Alkylene-bridged polysilsesquioxanes are hybrid xerogels whose organic bridging group is an integral constituent of the network polymer that can be systematically varied to probe the influence of its length on the xerogels' porosity and morphology. Our previous studies have shown that hexylene-bridged polysilsesquioxane xerogels prepared from 1, 6-bis(triethoxysilyl)hexane under acidic conditions are nonporous while the pentylene-bridged polysilsesquioxanes prepared under the same conditions are porous. We also discovered that the more reactive 1, 6-bis(trimethoxysilyl)hexane monomer could polymerize under acidic conditions to afford porous xerogels. Here, we have extended our study of bis(trimethoxysilyl)alkanes to include the heptylene (C7), octylene (C8), nonylene(C9) and decylene (C10) bridges so as to ascertain at what bridging group length the porosity collapses. The morphology of the resulting xerogels was characterized by nitrogen sorption porosimetry and electron microscopy. Solid state NMR was used to structurally characterize the materials.