Two dimensional eye tracking: Sampling rate of forcing function

A study was conducted to determine the minimum update rate of a forcing function display required for the operator to approximate the tracking performance obtained on a continuous display. In this study, frequency analysis was used to determine whether there was an associated change in the transfer function characteristics of the operator. It was expected that as the forcing function display update rate was reduced, from 120 to 15 samples per second, the operator's response to the high frequency components of the forcing function would show a decrease in gain, an increase in phase lag, and a decrease in coherence

Head tracking at large angles from the straight ahead position

One of the big advantages of a helmet sight in a high performance aircraft is its off-boresight capability in aiming a fire control system. However, tracking data using a target that is moving rapidly and randomly for an extended period of time is missing. This study is intended to provide data in this area that will be of value to engineers in designing head control systems

Breaking in and Busting out: Cell-penetrating Peptides and the Endosomal Escape Problem

Cell-penetrating peptides (CPPs) have long held great promise for the manipulation of living cells for therapeutic and research purposes. They allow a wide array of biomolecules from large, oligomeric proteins to nucleic acids and small molecules to rapidly and efficiently traverse cytoplasmic membranes. With few exceptions, if a molecule can be associated with a CPP, it can be delivered into a cell. However, a growing realization in the field is that CPP-cargo fusions largely remain trapped in endosomes and are eventually targeted for degradation or recycling rather than released into the cytoplasm or trafficked to a desired subcellular destination. This ‘endosomal escape problem’ has confounded efforts to develop CPP-based delivery methods for drugs, enzymes, plasmids, etc. This review provides a brief history of CPP research and discusses current issues in the field with a primary focus on the endosomal escape problem, for which several promising potential solutions have been developed. Are we on the verge of developing technologies to deliver therapeutics such as siRNA, CRISPR/Cas complexes and others that are currently failing because of an inability to get into cells, or are we just chasing after another promising but unworkable technology? We make the case for optimism

Observation of neutral sulfuric acid-amine containing clusters in laboratory and ambient measurements

Recent ab initio calculations showed that amines can enhance atmospheric sulfuric acid-water nucleation more effectively than ammonia, and this prediction has been substantiated in laboratory measurements. Laboratory studies have also shown that amines can effectively displace ammonia in several types of ammonium clusters. However, the roles of amines in cluster formation and growth at a microscopic molecular scale (from molecular sizes up to 2 nm) have not yet been well understood. Processes that must be understood include the incorporation of amines into sulfuric acid clusters and the formation of organic salts in freshly nucleated particles, which contributes significantly to particle growth rates. We report the first laboratory and ambient measurements of neutral sulfuric acid-amine clusters using the Cluster CIMS, a recently-developed mass spectrometer designed for measuring neutral clusters formed in the atmosphere during nucleation. An experimental technique, which we refer to as Semi-Ambient Signal Amplification (SASA), was employed. Sulfuric acid was added to ambient air, and the concentrations and composition of clusters in this mixture were analyzed by the Cluster CIMS. This experimental approach led to significantly higher cluster concentrations than are normally found in ambient air, thereby increasing signal-to-noise levels and allowing us to study reactions between gas phase species in ambient air and sulfuric acid containing clusters. Mass peaks corresponding to clusters containing four H<sub>2</sub>SO<sub>4</sub> molecules and one amine molecule were clearly observed, with the most abundant sulfuric acid-amine clusters being those containing a C2- or C4-amine (i.e. amines with masses of 45 and 73 amu). Evidence for C3- and C5-amines (i.e. amines with masses of 59 and 87 amu) was also found, but their correlation with sulfuric acid tetramer was not as strong as was observed for the C2- and C4-amines. The formation mechanisms for those sulfuric acid-amine clusters were investigated by varying the residence time in the inlet. It was concluded that the amines react directly with neutral clusters and that ion-induced clustering of sulfuric acid cluster ions with amines was not a dominant process. Results from ambient measurements using the Cluster CIMS without addition of sulfuric acid have shown that the sulfuric acid-amine clusters were reasonably well correlated with sulfuric acid tetramer and consistent with the SASA experiments at the same Boulder sampling site. Also, clusters that contain C2- or C4-amines were more abundant and better correlated with sulfuric acid tetramer than other types of amine containing clusters. However, ambient measurements of sulfuric acid-amine clusters remain difficult and highly uncertain because their concentrations are only slightly above background levels, even during nucleation events

EFN-4 Functions in LAD-2-mediated Axon Guidance in Caenorhabditis elegans

During development of the nervous system, growing axons rely on guidance molecules to direct axon pathfinding. A well-characterized family of guidance molecules are the membrane-associated ephrins, which together with their cognate Eph receptors, direct axon navigation in a contact-mediated fashion. InC. elegans, the ephrin-Eph signaling system is conserved and is best characterized for their roles in neuroblast migration during early embryogenesis. This study demonstrates a role for theC. elegansephrin EFN-4 in axon guidance. We provide both genetic and biochemical evidence that is consistent with theC. elegansdivergent L1 cell adhesion molecule LAD-2 acting as a non-canonical ephrin receptor to EFN-4 to promote axon guidance. We also show that EFN-4 probably functions as a diffusible factor because EFN-4 engineered to be soluble can promote LAD-2-mediated axon guidance. This study thus reveals a potential additional mechanism for ephrins in regulating axon guidance and expands the repertoire of receptors by which ephrins can signal