Water desorption in Kelvin-probe force microscopy: a generic model.

Nanoparticles or similar, nanoscale objects such as proteins or biological fibrils usually have to be deposited from aqueous suspension onto a solid support surface for further characterization by atomic force microscopy (AFM) and related methods such as Kelvin-probe force microscopy (KFM). Here we show, on the examples of functionalized nanoparticles and collagen fibrils, that water desorption after sample preparation affects their electrostatic potential determined by KFM in a predictable manner. We explain this effect with a simple, analytical model based on the capacitance of the partially dielectric-filled tip-sample system. We also propose practical measures to avoid false interpretation of electrical AFM-based experiments. As the phenomenon is very generic it may have significant implications in the application of AFM to nanoparticles and other nanostructures including biological ones.

Organic farming in the corn belt.

A small minority of farmers in the Midwest produces crops on a commercial scale without using modern fertilizers and pesticides. On the basis of a 5-year study, it appears that these farmers have more in common with the majority of farmers in the region than with certain stereotypes of organic farmers. Their farming practices (other than chemical use), the size and labor requirements of their farms, and the production and profitability they achieve differ from those of conventional farmers by considerably less than might be expected on the basis of the fundamental importance of chemicals in modern agricultural production. Compared to conventional methods, organic methods consume less fossil energy and cause less soil erosion, but have mixed effects on soil nutrient status and grain protein content.

Fertilizer nitrogen: contribution to nitrate in surface water in a corn belt watershed.

Measurements of nitrate concentration and relative enrichment in nitrogen-15 were made on samples of the surface waters of a typical Illinois corn belt watershed and the effluent of the subterranean tiles that drain the cropped land in the region. From these measurements, we estimate that at the time of peak nitrate concentration in the spring of 1970 a minimum of 55 to 60 percent of the nitrogen found as nitrate in the surface waters of this watershed originated from fertilizer nitrogen

Signal reversal in Kelvin-probe force microscopy.

Kelvin-probe force microscopy is a measurement mode of atomic force microscopy, which is used to quantitatively map the electrical surface potential of a sample. Inadequate hardware and electronic design can lead to signal cross talk and, in consequence, false results. Here, we show that certain cross talk artifacts not only do manifest themselves in additional noise, reduced resolution, or an offset of the measured surface potential but can also lead to an inverted signal scale and, crucially, cannot be diagnosed with a known reference signal. We show experimental data on an electrically homogeneous sample, describe a method to detect the artifact, and propose simple remedies, which should be well within the reach of most research and industrial laboratories.

Mutations in the STAT5A gene are associated with embryonic survival and milk composition in cattle.

The objective of this study was to investigate the association of the signal transducer and activator of transcription 5A (STAT5A) gene with fertilization rate, embryonic survival, and milk production and composition in cattle. The STAT proteins are transcription factors that are specifically activated to regulate gene transcription when cells encounter cytokines and growth factors. The STAT5A gene is a member of the interferon-tau (IFN-tau) and placental lactogen (PL) signaling pathway, which is involved in both milk production and initiation of pregnancy. Using the DNA-pooling sequencing approach, a total of 12 single nucleotide polymorphisms (SNP) were identified, 1 exonic and 11 intronic. For the study of association of these SNP with embryonic survival, 1,551 embryos were produced in vitro from 160 cows and 3 sires. Significant associations with embryonic survival were found for 7, 5, and 2 SNP for embryos produced from sires 1, 2, and 3 respectively. The association of fertilization rate with STAT5A polymorphisms was evaluated in more than 2,300 oocytes. Significant associations were found for 6, 2, and 2 SNP for sires 1, 2, and 3 respectively. For sire 1, 5 SNP showed significant associations with both embryonic survival and fertilization rate compared with 1 SNP for sires 2 and 3. To determine if embryonic losses had occurred before the blastocyst stage, 145 of the surviving embryos were harvested at d 7 of development and genotyped for the single exonic SNP12195. A significant segregation distortion was observed between oocytes produced from 2 sires carrying the same genotype. Thus, it is most likely that STAT5A is associated with 2 mechanisms of embryo death. One is a prefertilization mechanism involving sperm factors that cause low fertilization rate. The second is a postfertilization mechanism that causes incompatibility between the male pronucleus and the oocyte, which in turn leads to death of the embryo before the blastocyst stage. Association testing of SNP12195 (exon 8) and SNP14217 (intron 9) with milk composition revealed that allele G of SNP12195 was associated with a decrease in both protein and fat percentages. However, SNP14217 in intron 9 showed no significant association with milk production or health traits. The G allele of SNP12195 was also associated with low embryonic survival, making this SNP an attractive candidate for progeny testing programs in dairy cattle.

Active damping by Q-control for fast force-distance curve measurements in atomic force microscopy.

This paper investigates the benefit of active damping by an analog Q-control circuit for measuring fast force-distance curves in atomic force microscopy. By active damping of the cantilever oscillation after snap-off, the down-ring time-constant is reduced significantly from 385 µs to 23 µs. Experimental results demonstrate that the number of force-distance curves per second can be increased by a factor of more than 30.

Asymmetric distribution of left ventricular asynergy in coronary artery disease and its relation to coronary stenoses.

In 100 patients with coronary artery disease (CAD), the prevalence and severity of asynergy was determined for 9 left ventricular (LV) segments by both radionuclide and contrast angiography. The anterior, septal and lateral LV walls had significantly more prevalent and more severe asynergy in the medial segments than in the basal segments. In contrast, the inferior LV wall exhibited equally severe asynergy in both the medial and basal segments. In general, asynergy was most severe in the apical, medial septal, medial inferior and basal inferior LV segments. This asymmetric distribution of LV asynergy could not be explained by the distribution of occlusions or significant stenoses in the arterial tree, which were relatively uniformly distributed among the left anterior descending (32%), left circumflex (29%) and right (26%) coronary arteries. It is postulated instead that the asymmetric distribution of LV asynergy results from asymmetry of the coronary arterial tree supplying the left ventricle and that the prevalence of asynergy in an LV segment is directly related to its vascular distance from the coronary ostia. Unlike the relatively direct supply of the left anterior descending and circumflex arteries to the basal segments of the anterior, septal and lateral LV walls, the arterial supply to the basal inferior wall begins only after the right or dominant circumflex artery has traversed the length of the atrioventricular groove, significantly increasing its susceptibility to the pressure attenuation and occlusive jeopardy of more proximal stenoses.

Estimates of N2-fixation from variation in the natural abundance of 15N in Sonoran desert ecosystems.

The 15N abundance of tissues of five Prosopis specimens at our primary study site (a Prosopis woodland at Harper's Well in the Sonoran desert of Southern California) was determined over two growing seasons 1980 and 1981. The 15N abundance of soil and of tissues of presumed non-N2-fixing (control) plants was also measured. Prosopis tissues were significantly lower in 15N than either soil N or corresponding tissues of presumed non-N2-fixing plants which derive their N entirely from soil. Soil N was also significantly higher in 15N than atmospheric N2. We conclude that it is feasible to use variations in the natural abundance of 15N as an index of N2-fixation in this kind of ecosystem, and that N2-fixation is of considerable importance to Prosopis growing at this site.We also determined the 15N abundance of leaf tissue of presumed N2-fixing and control plants growing at the same site at six additional sites (five in the Sonoran desert of southern California and one in Baja California, Mexico near the town of Catavina). Four of these additional sites were dominated by Prosopis and two were mixed communities. There were statistically significant differences between the 15N abundances of the pooled legume population and control plants at all sites, although not every legume specimen exhibited this difference. From 15N abundance data we estimated the fractional contribution of biologically fixed N to the N economy of desert legumes. We concluded that N2-fixation is very important to Prosopis at six of seven sites in the Sonoran Desert. At the site where Prosopis did not appear to be fixing N2, N2-fixation was important only for legumes of the sub-family Papilionoideae, Lupinus, Dalea, Astragalus and Lotus.

Monoclonal antibodies to the GP5 of porcine reproductive and respiratory syndrome virus are more effective in virus neutralization than monoclonal antibodies to the GP4.

The arterivirus porcine reproductive and respiratory syndrome virus (PRRSV) contains six structural proteins the roles of which are not completely understood. In a preceding study, immunization with the dutch isolate I10 of PRRSV had led to the development of MAbs against four structural proteins [Wieczorek-Krohmer, M., 1994. Herstellung und Charakterisierung von monoklonalen Antikörpern gegen das Virus des Porzinen Reproduktiven und Respiratorischen Syndroms (PRRSV). Inaugural-Dissertation, Ludwig-Maximilians-Universität, München] here finally identified by reaction with individual plasmid-expressed PRRSV proteins as products of ORFs 3 (GP3), 4 (GP4), 5 (GP5) and 7 (N). Surprisingly, the MAbs against GP5 revealed the presence of two antigenically distinct virus populations in the isolate I10, the population PRRSV-'PPV', isolated from plaques and the PRRSV-'EPV', gained by end point dilution. MAbs against GP3, GP4 and N reacted with both I10 populations as well as with natural PRRSV isolates. However, the anti-GP5 MAbs exclusively recognized PRRSV-'PPV'. In this study immunization of mice with both separated I10 populations confirmed that solely PRRSV-'PPV' possesses the property to induce an immune response ultimately leading to the establishment of MAbs against GP5. Whereas the 15 anti-GP5 MAbs (derived from four independent fusions) reacted exclusively with PRRSV-'PPV' of the isolate I10, anti-GP4 MAbs detected their target antigen on various isolates of European origin and were able to neutralize them. As indicated by competition assays and selection of neutralization-resistant virus mutants, all GP5 MAbs are directed against a single antigenic site on the ORF 5 protein. Both groups of neutralizing antibodies bound to the surface of purified virions demonstrating that the recognized epitopes represent surface structures of the virion envelope. However, anti-GP5 MAbs mediated the binding of more gold granules than anti-GP4 MAbs. Comparison of the neutralizing effect of anti-GP4 and anti-GP5 MAbs revealed the anti-GP5 MAbs as the more efficient antibodies. For the complete neutralization of about 100 ID50 of PRRSV-'PPV' anti-GP5 culture supernatant was effective up to a dilution of 1:1280 whereas the most effective anti-GP4 antibodies exhibited a comparable effect only up to 1:64. These results indicate that PRRSV GP5 in principle is a major target for neutralizing antibodies, as is found for other arteriviruses, but that in nature 'ORF 5 escape mutants' may develop as easily as in vitro.

Porcine reproductive and respiratory syndrome virus (PRRSV): monoclonal antibodies detect common epitopes on two viral proteins of European and U.S. isolates.

Sixteen hybridoma cell lines secreting monoclonal antibodies (mAbs) directed against two dutch isolates of the causative virus of Porcine Reproductive and Respiratory Syndrome (PRRSV) were produced. The hybridoma cells resulted from fusions of SP2/0 myeloma cells with splenocytes of STU mice immunized with purified PRRSV after induction of immunotolerance against host cell constituents. Screening of supernatant fluids was performed by an indirect immunofluorescence assay on PRRSV-infected porcine alveolar macrophages. Immunoblotting studies revealed that the mAbs had different protein specificities. One mAb reacted with a viral 15 kD protein, eleven were directed against a 40-50 kD protein, and four against a 30-40 kD protein. The mAb against the 15 kD putative nucleocapsid protein as well as five mAbs against the 40-50 kD protein recognized epitopes on these proteins which are conserved in various European and U.S. isolates of PRRSV.

Naive physics: the curvilinear impetus principle and its role in interactions with moving objects.

Several recent studies in which subjects solved pencil-and-paper problems concerning the behavior of moving objects have shown that many people have incorrect beliefs about motion. The present study considers the question of whether these naive beliefs are manifested in situations where people observe and interact with moving objects. Several findings in the problem-solving literature suggest that abstract or unrealistic tasks may fail to tap knowledge and reasoning abilities that are routinely used in more concrete or realistic situations. Thus, most people may have accurate knowledge about the behavior of moving objects, knowledge that they use in their everyday interactions with objects in motion. However, this knowledge may not be activated in the context of abstract, static problems, and as a result people attempting to solve such problems may resort to naive beliefs. Three experiments examine this possibility in the context of one specific naive belief, the curvilinear impetus belief. Contrary to expectations, results suggest that the curvilinear impetus belief is used not only on pencil-and-paper problems but also in situations where people observe and interact with moving objects. Implications of these findings are discussed.

Team treatment of eating disorders.

The treatment of eating disorders requires the expertise of a multidisciplinary team. This case presents the psychologic and physiologic challenges observed in managing these patients. Attention must be directed toward the use of techniques to obtain a commitment from patients to meet a therapeutic goal. Care must be taken to avoid overaggressive feeding of patients with eating disorders to avoid the refeeding syndrome.

Survey of naturally and conventionally cured commercial frankfurters, ham, and bacon for physio-chemical characteristics that affect bacterial growth.

Natural and organic food regulations preclude the use of sodium nitrite/nitrate and other antimicrobials for processed meat products. Consequently, processors have begun to use natural nitrate/nitrite sources, such as celery juice/powder, sea salt, and turbinado sugar, to manufacture natural and organic products with cured meat characteristics but without sodium nitrite. The objective of this study was to compare physio-chemical characteristics that affect Clostridium perfringens and Listeria monocytogenes growth in naturally cured and traditionally cured commercial frankfurters, hams, and bacon. Correlations of specific product characteristics to pathogen growth varied between products and pathogens, though water activity, salt concentration, and product composition (moisture, protein and fat) were common intrinsic factors correlated to pathogen growth across products. Other frequently correlated traits were related to curing reactions such as % cured pigment. Residual nitrite and nitrate were significantly correlated to C. perfringens growth but only for the ham products.

Inhibition of Listeria monocytogenes using natural antimicrobials in no-nitrate-or-nitrite-added ham.

Consumer demand for foods manufactured without the direct addition of chemical preservatives, such as sodium nitrite and organic acid salts, has resulted in a unique class of "naturally" cured meat products. Formulation with a natural nitrate source and nitrate-reducing bacteria results in naturally cured processed meats that possess traits similar to conventionally cured meats. However, previous research has shown that the naturally cured products are more susceptible to pathogen growth. This study evaluated Listeria monocytogenes growth on ham manufactured with natural curing methods and with commercially available clean-label antimicrobials (cultured sugar and vinegar blend; lemon, cherry, and vinegar powder blend) and assessed impacts on physicochemical characteristics of the product. Hams made with either of the antimicrobials supported L. monocytogenes growth similar to that in the traditionally cured control (P > 0.05). Hams made with prefermented celery juice powder had the lowest residual nitrite concentrations (P < 0.05), and when no antimicrobial was added, L. monocytogenes growth was similar to that of the uncured control (P > 0.05). Aside from residual nitrite and nitrate concentrations, few physicochemical differences were identified. These findings show that ham can be produced with natural curing methods and antimicrobials to provide similar L. monocytogenes inhibition and physicochemical traits as in traditionally cured ham.