Tandem Mobility Mass Spectrometry Study of Electrosprayed Tetraheptyl Ammonium Bromide Clusters

Multiply charged electrospray ions from concentrated solutions of Heptyl4N+Br− (designated A+B− hereafter) in formamide are analyzed mass spectrometrically (MS) following mobility selection in ambient air in a differential mobility analyzer (DMA). Most of the sharp mobility peaks seen are identified as (AB)nA+ clusters, with 0 ≤ n ≤ 5. One anomalously abundant and mobile ion is identified as NH4+(AB)4. Six ions in the (AB)n(A+)2 series are also identified, completing and correcting earlier mobility data for singly and doubly charged ions up to masses of almost 9000 Da. The more mobile of two broad humps seen in the mobility spectrum includes m/z values approximately from 2500 up to 12,000 Da. It is formed primarily by multiply charged (AB)n(A+)z clusters with multiple ammonium bromide adducts. Because of overlapping of many peaks of different m/z and charge state z, only a few individual species can be identified by MS alone in this highly congested region. However, the spectral simplification brought about by mobility selection upstream of the MS reveals a series of broad modulations in m/z space, with all ions resolved in the second, third, …sixth modulation being in charge states z = 2, 3, …6, respectively. Extrapolation of this trend beyond the sixth wave fixes the ion charge state (in some cases up to z = 15) and mass (beyond m = 175,000 u). This wavy structure had been previously observed and explained in terms of ion evaporation kinetics from volatile drops, though without mass identification. All observations indicate that the clusters are formed as charged residues, but their charge state is fixed by the Iribarne-Thomson ion evaporation mechanism. Consequently, the measured curve of cluster diameter versus z yields the two parameters governing ion evaporation kinetics. Clusters with z > 1 and electrical mobility Z > 0.495 cm2/V/s are metastable and evaporate a singly charged cluster, probably (AB)2A+, between the DMA and the MS. Plotting the electrical mobilities Z of the clusters in the form (z/Z)1/2 versus m1/3 (both proportional to cluster diameter) collapse the data for all cluster sizes and charge states into one single straight line for Z below 0.495 cm2/V/s. This linear relation reveals a uniform apparent cluster density of 0.935 g/cm3 and an effective hard-sphere diameter of the air molecules of 0.44 nm. An anomalous mobility increase is observed at diameters below 3 nm

Multiancestry analysis of the HLA locus in Alzheimer’s and Parkinson’s diseases uncovers a shared adaptive immune response mediated by HLA-DRB1*04 subtypes

Across multiancestry groups, we analyzed Human Leukocyte Antigen (HLA) associations in over 176,000 individuals with Parkinson’s disease (PD) and Alzheimer’s disease (AD) versus controls. We demonstrate that the two diseases share the same protective association at the HLA locus. HLA-specific fine-mapping showed that hierarchical protective effects of HLA-DRB1*04 subtypes best accounted for the association, strongest with HLA-DRB1*04:04 and HLA-DRB1*04:07, and intermediary with HLA-DRB1*04:01 and HLA-DRB1*04:03. The same signal was associated with decreased neurofibrillary tangles in postmortem brains and was associated with reduced tau levels in cerebrospinal fluid and to a lower extent with increased Aβ42. Protective HLA-DRB1*04 subtypes strongly bound the aggregation-prone tau PHF6 sequence, however only when acetylated at a lysine (K311), a common posttranslational modification central to tau aggregation. An HLA-DRB1*04-mediated adaptive immune response decreases PD and AD risks, potentially by acting against tau, offering the possibility of therapeutic avenues

2007 Induction charge detector with multiple sensing stages

An induction charge detector yields the net charge and the time of flight of a particle. The unique ability to independently measure these two parameters sets apart this rather simple detection technique. The main shortcoming of this instrument is its high charge detection limit, resulting from the intrinsic noise of the detector electronics and the low signal associated with the charge to measure. The goal of the present work is to lower the detection limit of this detector. This article describes an induction charge detector whose main novelty is a sequence of aligned cylindrical electrodes for measuring the charge of a particle n times. In a time domain analysis, this feature reduces both the detection limit and the standard error of the charge measurement by factors of ͱ 2 and ͱ n. More importantly, sensing stages could be added to arbitrarily lower the detection limit in a frequency domain analysis

Characterization of Electrosprays and Its Relevance to Colloid Thrusters

In this article we use a combination of energy analysis and time of flight techniques to measure a set of electrofluiddynamic parameters that are relevant to electrosprays in the cone-jet mode. Knowledge of the voltage difference between electrospraying needle and the point at which charged droplets are formed, the initial velocity of the droplets and their specific charge distribution function, is essential to comprehend properties of the Colloid thruster such as its thrusting efficiency. We find that a large fraction of the electrospray needle voltage is used to accelerate the jet, and the pressure of the jet's fluid at the breakup point is negligible as compared to its specific kinetic energy. We expect that these measurements will guide the analytical modeling of cone-jets, which is necessary to understand the performance of Colloid thrusters

Microfabricated electrospray thruster array with high hydraulic resistance channels

Electrospray thrusters can deliver the efficient primary propulsion and attitude control actuation needed by small satellites. The microfabricated multiemitter array is an ideal implementation of this technology because it addresses the thrust, volume, mass, and scalability requirements across the size range of small satellites. This paper describes the microfabrication and testing of an internally fed 64-emitter array. The main goal is to decouple the design and fabrication of the emitters from the need to provide a flowpath with sufficient hydraulic resistance for each emitter. The latter has traditionally been achieved by reducing the diameter of the emitter’s inner channel or by filling it with a bed of beads; whereas in this paper, individual flow-restrictive channels are etched on the back of the emitter wafer, connecting each emitter to a common distribution manifold. The source operates steadily in vacuum. Beam interception by the extractor is negligible in a wide range of flow rates and emitter potentials. The thrust, mass flow rate, specific impulse, and propulsive efficiency are calculated using the time-of-flight technique. These parameters range between 8.1 and 54.0  μN, 3.5×10−9 and 5.73×10−8  kg/s, 96 and 236 s, and 61 and 75% using the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide as propellant

Fast etching of microscale structures by bombardment with electrosprayed nanodroplets

In this article Si substrates protected by Shipley 1827 and Au masks are sputtered with electrosprayed nanodroplets to produce microscale structures. Silicon is used as a benchmark to assess the effect of the physical sputtering of nanodroplets on more interesting chemically inert materials such as SiC and GaN. The use of Shipley 1827 as a patterning mask provides a virtually infinite etching selectivity between substrate and photoresist at the cost of non-perpendicular wall profiles and debris redeposition. After 60 minutes of processing the target at a sputtering rate of 244 nm/min, a fraction of the sputtered material deposits back on the substrate forming a protective layer that stops any further sputtering. In a second set of experiments the selectivity between Si and Au to be used as a potential mask is studied. The maximum selectivity is 64.17, and is obtained at an etching rate of 385 nm/min. An increase of the etching rate produces a sharp drop on the selectivity between Au and Si

Hall Thrusters Operating in Pulsed Mode

Heretofore, Hall thrusters were perceived as strictly steady state devices, unsuitable for operation in a pulsed mode. We have demonstrated that at least certain types of Hall thrusters can efficiently deliver thrust pulses with a duration as short as few tens of msec. Our 200 W Hall thruster, designated BHT-200, was pulsed nearly 500,000 times delivering precisely controllable, repetitive impulse bits of arbitrary magnitude starting as low as sub mNsec. This was achieved without significant loss of efficiency and a moderate loss of specific impulse due to xenon flow timing. The thruster was driven by both a PPU and by discharging a capacitor in the so called direct drive pioneered by others. This demonstration opens a new field of applicability for the tandem style and possibly other Hall thrusters that was previously reserved to PPTs and cold gas thrusters. This includes attitude control and primary propulsion for microspacecraft that lack sufficient power for continuous operation at 200 W. For spacecraft with sufficient power on board, the same Hall thruster can be used for both primary and ACS propulsion. The paper treats the subject in a generic manner describing the various methods of pulsed mode operation, flow and electrical start-up transients, system requirements and areas of applicability. This description is supported by analytical models and data from the pulsed BHT-200 experiments. Introduction and Pulsed Hall Thruster Applications Heretofore, Hall thrusters were perceived as devices suitable only for steady state operation. As will be described in this paper we have demonstrated that at least some types of Hall thrusters can be pulsed with a pulse duration as short as few tens of msec and deliver nearly steady state performance. Busek's 200 W tandem style Hall thruster demonstrated that it can efficiently produce impulses ranging from a mNsec to nearly infinity, limited only by its lifetime. For the variable impulse it can be powered by a conventional PPU, capacitor discharge thus eliminating conventional PPU, and in some configurations directly from solar panels. With advanced capacitors the necessary energy can be stored in 1-in cube. With these capabilities and lower complexity/cost of some configurations, a whole new range of applications emerges that includes propulsion for power limited micro or nano spacecraft, ACS (attitude control system) propulsion for large spacecraft that already have Xe on board and general, combined steady state and pulsed thrusting using the same Hall thruster on a wide variety of spacecraft. These applications are briefly discussed below