393 research outputs found
Type II secretion: from structure to function
Gram-negative bacteria use the type II secretion system to transport a large number of secreted proteins from the periplasmic space into the extracellular environment. Many of the secreted proteins are major virulence factors in plants and animals. The components of the type II secretion system are located in both the inner and outer membranes where they assemble into a multi-protein, cell-envelope spanning, complex. This review discusses recent progress, particularly newly published structures obtained by X-ray crystallography and electron microscopy that have increased our understanding of how the type II secretion apparatus functions and the role that individual proteins play in this complex system.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74575/1/j.1574-6968.2006.00102.x.pd
Towards Quantum Sensing of Chiral-Induced Spin Selectivity: Probing Donor-Bridge-Acceptor Molecules with NV Centers in Diamond
Photoexcitable donor-bridge-acceptor (D-B-A) molecules that support
intramolecular charge transfer are ideal platforms to probe the influence of
chiral-induced spin selectivity (CISS) in electron transfer and resulting
radical pairs. In particular, the extent to which CISS influences spin
polarization or spin coherence in the initial state of spin-correlated radical
pairs following charge transfer through a chiral bridge remains an open
question. Here, we introduce a quantum sensing scheme to measure directly the
hypothesized spin polarization in radical pairs using shallow nitrogen-vacancy
(NV) centers in diamond at the single- to few-molecule level. Importantly, we
highlight the perturbative nature of the electron spin-spin dipolar coupling
within the radical pair, and demonstrate how Lee-Goldburg decoupling can
preserve spin polarization in D-B-A molecules for enantioselective detection by
a single NV center. The proposed measurements will provide fresh insight into
spin selectivity in electron transfer reactions.Comment: 7 pages and 4 pages appendix including an extensive description of
the initial spin state of photo-generated radical pair
Quantifying the Effect of Pyraclostrobin on Grainfill Period and Kernel Dry Matter Accumulation in Maize
Strobilurin fungicides are effective against a wide range of foliar fungal diseases on several crops and may offer additional physiological benefits, including plants staying green longer than normal (the stay-green effect ). It has been hypothesized that the stay-green effect may extend the grain fill period leading to increased grain yield due to a longer period of dry matter accumulation. We investigated the effect of pyraclostrobin fungicide applied at tasseling on foliar disease suppression, stalk rot severity, the stay-green effect of leaves in the upper canopy, dry matter accumulation, time at physiological maturity, grain yield, and moisture at harvest in maize from 2008 through 2010 in Iowa at six location years. Foliar disease severity was0.1) between pyraclostrobin-treated and non-treated maize in all location years, treated plots tended to have higher yield and grain moisture. Time at physiological maturity did not differ between pyraclostrobin-treated and nontreated plots (P \u3e 0.1). Although we demonstrated an application of pyraclostrobin to maize delayed senescence of the leaves thus contributing to the stay-green effect, our data did not show grain-fill period extension
Spatially resolved surface dissipation over metal and dielectric substrates
We report spatially resolved measurements of static and fluctuating electric
fields over conductive (Au) and non-conductive (SiO2) surfaces. Using an
ultrasensitive `nanoladder' cantilever probe to scan over these surfaces at
distances of a few tens of nanometers, we record changes in the probe resonance
frequency and damping that we associate with static and fluctuating fields,
respectively. We find that the two quantities are spatially correlated and of
similar magnitude for the two materials. We quantitatively describe the
observed effects on the basis of trapped surface charges and dielectric
fluctuations in an adsorbate layer. Our results provide direct, spatial
evidence for surface dissipation in adsorbates that affects nanomechanical
sensors, trapped ions, superconducting resonators, and color centers in
diamond
Single Nitrogen-Vacancy-NMR of Amine-Functionalized Diamond Surfaces
Nuclear magnetic resonance (NMR) imaging with shallow nitrogen-vacancy (NV)
centers in diamond offers an exciting route toward sensitive and localized
chemical characterization at the nanoscale. Remarkable progress has been made
to combat the degradation in coherence time and stability suffered by
near-surface NV centers using suitable chemical surface termination. However,
approaches that also enable robust control over adsorbed molecule density,
orientation, and binding configuration are needed. We demonstrate a diamond
surface preparation for mixed nitrogen- and oxygen-termination that
simultaneously improves NV center coherence times for emitters <10-nm-deep and
enables direct and recyclable chemical functionalization via amine-reactive
crosslinking. Using this approach, we probe single NV centers embedded in
nanopillar waveguides to perform NMR sensing of covalently
bound trifluoromethyl tags in the ca. 50-100 molecule regime. This work
signifies an important step toward nuclear spin localization and structure
interrogation at the single-molecule level.Comment: 21 pages and 16 pages supporting informatio
Diamond surface engineering for molecular sensing with nitrogen-vacancy centers
Quantum sensing using optically addressable atomic-scale defects, such as the
nitrogen--vacancy (NV) center in diamond, provides new opportunities for
sensitive and highly localized characterization of chemical functionality.
Notably, near-surface defects facilitate detection of the minute magnetic
fields generated by nuclear or electron spins outside of the diamond crystal,
such as those in chemisorbed and physisorbed molecules. However, the promise of
NV centers is hindered by a severe degradation of critical sensor properties,
namely charge stability and spin coherence, near surfaces (< ca. 10 nm deep).
Moreover, applications in the chemical sciences require methods for covalent
bonding of target molecules to diamond with robust control over density,
orientation, and binding configuration. This forward-looking Review provides a
survey of the rapidly converging fields of diamond surface science and
NV-center physics, highlighting their combined potential for quantum sensing of
molecules. We outline the diamond surface properties that are advantageous for
NV-sensing applications, and discuss strategies to mitigate deleterious effects
while simultaneously providing avenues for chemical attachment. Finally, we
present an outlook on emerging applications in which the unprecedented
sensitivity and spatial resolution of NV-based sensing could provide unique
insight into chemically functionalized surfaces at the single-molecule level.Comment: Review paper, 36 page
Drainage Water Storage for Improved Resiliency and Environmental Performance of Agricultural Landscapes
Drained lands, which include some of the most productive lands in the world, can experience both water excess and water deficit within a year. Storing drained water within the landscape could increase the sustainability of water for agriculture, particularly as intense rainfall and prolonged summer drought continue to increase under future climate change. A team of researchers and extension specialists from nine states are currently working towards a vision of transforming the process of designing and implementing agricultural drainage to include storage through the use of controlled drainage, saturated buffers, and drainage water recycling (i.e. capture, storage, and reuse). Field research data from experimental drainage sites from across the U.S. Corn Belt have been brought together in a database to support synthesis and modeling to determine economic and environmental impacts of drainage water storage. Results from this effort will extend the strategies and tools to agricultural producers, the drainage industry, watershed managers, agencies, and policy makers, and educate the next generation of engineers and scientists to design drainage systems that include water storage in the landscape
Maize Leaf Appearance Rates: A Synthesis From the United States Corn Belt
The relationship between collared leaf number and growing degree days (GDD) is crucial for predicting maize phenology. Biophysical crop models convert GDD accumulation to leaf numbers by using a constant parameter termed phyllochron (°C-day leafâ1) or leaf appearance rate (LAR; leaf oC-dayâ1). However, such important parameter values are rarely estimated for modern maize hybrids. To fill this gap, we sourced and analyzed experimental datasets from the United States Corn Belt with the objective to (i) determine phyllochron values for two types of models: linear (1-parameter) and bilinear (3-parameters; phase I and II phyllochron, and transition point) and (ii) explore whether environmental factors such as photoperiod and radiation, and physiological variables such as plant growth rate can explain variability in phyllochron and improve predictability of maize phenology. The datasets included different locations (latitudes between 48° N and 41° N), years (2009â2019), hybrids, and management settings. Results indicated that the bilinear model represented the leaf number vs. GDD relationship more accurately than the linear model (R2 = 0.99 vs. 0.95, n = 4,694). Across datasets, first phase phyllochron, transition leaf number, and second phase phyllochron averaged 57.9 ± 7.5°C-day, 9.8 ± 1.2 leaves, and 30.9 ± 5.7°C-day, respectively. Correlation analysis revealed that radiation from the V3 to the V9 developmental stages had a positive relationship with phyllochron (r = 0.69), while photoperiod was positively related to days to flowering or total leaf number (r = 0.89). Additionally, a positive nonlinear relationship between maize LAR and plant growth rate was found. Present findings provide important parameter values for calibration and optimization of maize crop models in the United States Corn Belt, as well as new insights to enhance mechanisms in crop models
Metabolic and hormonal studies of Type 1 (insulin-dependent) diabetic patients after successful pancreas and kidney transplantation
Long-term normalization of glucose metabolism is necessary to prevent or ameliorate diabetic complications. Although pancreatic grafting is able to restore normal blood glucose and glycated haemoglobin, the degree of normalization of the deranged diabetic metabolism after pancreas transplantation is still questionable. Consequently glucose, insulin, C-peptide, glucagon, and pancreatic polypeptide responses to oral glucose and i.v. arginine were measured in 36 Type 1 (insulin-dependent) diabetic recipients of pancreas and kidney allografts and compared to ten healthy control subjects. Despite normal HbA1 (7.2±0.2%; normal <8%) glucose disposal was normal only in 44% and impaired in 56% of the graft recipients. Normalization of glucose tolerance was achieved at the expense of hyperinsulinaemia in 52% of the subjects. C-peptide and glucagon were normal, while pancreatic polypeptide was significantly higher in the graft recipients. Intravenous glucose tolerance (n=21) was normal in 67% and borderline in 23%. Biphasic insulin release was seen in patients with normal glucose tolerance. Glucose tolerance did not deteriorate up to 7 years post-transplant. In addition, stress hormone release (cortisol, growth hormone, prolactin, glucagon, catecholamines) to insulin-induced hypoglycaemia was examined in 20 graft recipients and compared to eight healthy subjects. Reduced blood glucose decline indicates insulin resistance, but glucose recovery was normal, despite markedly reduced catecholamine and glucagon release. These data demonstrate the effectiveness of pancreatic grafting in normalizing glucose metabolism, although hyperinsulinaemia and deranged counterregulatory hormone response are observed frequently
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A very thin havar film vacuum window for heavy ions to perform radiobiology studies at the BNL Tandem
Heavy ion beams from the BNL Tandem Van de Graaff accelerators will be made available for radiobiology studies on cell cultures. Beam energy losses need to be minimized both in the vacuum window and in the air in order to achieve the ranges required for the cells to be studied. This is particularly challenging for ions heavier than iron. The design is presented of a 0.4-inch diameter Havar film window that will satisfy these requirements. Films as thin as 80 microinches were successfully pressure tested. The final thickness to be used may be slightly larger to help in achieving pin hole free windows. We discuss design considerations and present pressure and vacuum test results as well as tests with heavy ion beams
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