Peak Coalescence Research Articles

Estimating major merger rates and spin parameters ab initio via the clustering of critical events

Abstract We build a model to predict from first principles the properties of major mergers. We predict these from the coalescence of peaks and saddle points in the vicinity of a given larger peak, as one increases the smoothing scale in the initial linear density field as a proxy for cosmic time. To refine our results, we also ensure, using a suite of ∼400 power-law Gaussian random fields smoothed at ∼30 different scales, that the relevant peaks and saddles are topologically connected: they should belong to a persistent pair before coalescence. Our model allows us to (a) compute the probability distribution function of the satellite-merger separation in Lagrangian space: they peak at three times the smoothing scale; (b) predict the distribution of the number of mergers as a function of peak rarity: haloes typically undergo two major mergers (>1:10) per decade of mass growth; (c) recover that the typical spin brought by mergers: it is of the order of a few tens of percent.

Crowd control of ions in the Astral analyzer.

Space charge effects are the Achilles' heel of all high-resolution ion optical devices. In time-of-flight mass analyzers, these may manifest as reduction of resolving power, mass measurement shift, peak coalescence, and/or transmission losses, while highly sensitive modern ion sources and injection devices ensure that such limits are easily exceeded. Space charge effects have been investigated, by experiment and simulation study, for the astral multi-reflection analyzer, incorporating ion focusing via a pair of converging ion mirrors, and fed by a pulsed extraction ion trap. Major factors were identified as the resonant effect between ~103 ions of similar m/z in-flight and the expansion of trapped packets of ~104-5 ions prior to extraction. Optimum operation and compensated ion mirror calibration strategies were then generated and described based on these findings.

An NMR-based approach for the design of crystallization processes for rigid molecules and effects of molecular rigidity and impurities on crystallization pathways

A methodology based on NMR analysis to enable development of crystallization procedures for relatively rigid molecules is presented. The number of relatively stable conformers in solution and their relative proportions are determined from peak splitting of equivalent protons and their relative areas as measured by NMR. Experimental data indicated that slow conformational interconversion was limiting crystallization at low temperatures. Variable temperature NMR analysis was utilized to determine rotamers’ peak coalescence and identify a suitable crystallization solvent. This NMR-based approach led to the development of a manufacturing crystallization recipe of a relatively rigid molecule that was impossible to crystallize via a scalable process. Furthermore, prediction of relatively stable conformer in gas phase, determined by Molecular Dynamics (MD) calculations were in acceptable agreement with data obtained from NMR analyses. Finally, the effects of molecular rigidity and impurities on crystallization and oiling-out pathways are described and an approach to avoid oiling-out is presented.

Dynamics of Interlayer Na-Ions in Ga-Substituted Na2Zn2TeO6 (NZTO) Studied by Variable-Temperature Solid-State 23Na NMR Spectroscopy and DFT Modeling.

Local Na-coordination and dynamics of Na2-xZn2-xGaxTeO6; x = 0.00 (NZTO), 0.05, 0.10, 0.15, 0.20, were studied by variable-temperature, 23Na NMR methods and DFT AIMD simulations. Structure and dynamics were probed by NMR in the temperature ranges of 100-293 K in a magnetic field of 18.8 T and from 293 up to 500 K in a magnetic field of 11.7 T. Line shapes and T1 relaxation constants were analyzed. At 100 K, the otherwise dynamic Na-ions are frozen out on the NMR time scale, and a local structure characterization was performed for Na-ions at three interlayer sites. On increasing the temperature, complex peak shape coalescences occurred, and at 293 K, the Na NMR spectra showed some averaging due to Na-ion dynamics. A further increase to 500 K did not reveal any new peak shape variations until the highest temperatures, where an apparent peak splitting was observed, similar to what was observed in the 18.8 T experiments at lower temperatures. A three-site exchange model coupled with reduced quadrupolar couplings due to dynamics appear to explain these peak shape observations. The Ga substitution increases the Na-jumping rate, as proved by relaxation measurements and by a decrease in temperature for peak coalescence. The estimated activation energy for Na dynamics in the NZTO sample, from relaxation measurements, corresponds well to results from DFT AIMD simulations. Upon Ga substitution, measured activation energies are reduced, which is supported, in part, by DFT calculations. Addressing the correlated motion of Na-ions appears important for solid-state ion conductors since benefits can be gained from the decrease in activation energy upon Ga substitution, for example.

Peak strength, coalescence and failure processes of rock-like materials containing preexisting joints and circular holes under uniaxial compression: Experimental and numerical study

The stability of rock masses is greatly influenced by the voids and joints present in rock masses; therefore, the peak strength, coalescence and failure process of rock masses with preexisting joints and holes should be systematically studied. To investigate the mechanical properties and failure mechanism of rock masses with circular holes and preexisting joints, rock-like materials were prepared, and uniaxial compression tests were performed. An analysis of physical test results showed that the coalescence patterns of rock bridges can be classified into 6 types, and the failure modes have 3 types. To further study the mechanical characteristics of rock-like materials with preexisting joints and circular holes, PFC2D numerical simulations were conducted, and the Bayesian optimization method was applied to obtain the microparameters of the PFC2D models. Through analysis of the numerical simulation results, it was concluded that the failure process of the specimen can be divided into four stages: stage I, stage II, stage III and stage IV. No cracks appeared in stage I, and few cracks appeared in stage III and stage IV. In stage IV, the specimen broke, and a large number of cracks appeared. These studies can serve as an experimental and numerical basis for the stability and fracture analysis of rock masses with preexisting joints and circular holes.

Experimental and numerical study on peak strength, coalescence and failure of rock-like materials with two folded preexisting fissures

Natural preexisting fissures are often overlapped, and these preexisting fissures greatly influence the stability of rock mass engineering; hence, it is necessary to investigate the strength and mechanical behaviour of rock materials with folded preexisting fissures. In this paper, for rock-like materials containing two folded preexisting fissures at different inclination angles and undulation angles, the folded preexisting fissures were overlapped by several preexisting fissures at the ends. The peak strength, coalescence patterns and failure modes were comprehensively investigated. It can be clearly found that the peak strength monotonically increased with increasing of the inclination angle; however, the influence of the undulation angle on the peak strength is not obvious through comparison with the inclination. Four coalescence modes can be summarized, and the failure mode can be classified into two types. By combining the crack number-strain curve and stress–strain curve, the failure process of the specimen with two folded preexisting fissures can be divided into four stages. In stage I, no cracks were generated; subsequently, some cracks were generated in stage II; however, the increment of the crack number was small. Many microcracks appear mainly in stage III and stage IV.

Experimental Study of Rock-like Materials with Two Unequal Parallel Preexisting Fissures under Uniaxial Compression

Fissures substantially impact the engineering stability of rock masses, making research on rock masses with preexisting fissures essential for engineering activities. The development of specimens with different preexisting fissure types was examined in this study. Three different types of specimens with preexisting fissures can be broadly categorized: specimens with few preexisting fissures, specimens with multiple preexisting fissures, and specimens with preexisting fissures and other flaws. Uniaxial compression tests of specimens with preexisting fissures of two unequal lengths were conducted, and the influence of preexisting fissure angle, the distance between the two fissures and fissure length on the peak strength and coalescence mode of specimens were analyzed. A large preexisting fissure length significantly influenced the peak strength and coalescence, and the uniaxial compressive strength (UCS) values of the rock-like materials decreased. In contrast, increasing the long preexisting fissure length influenced the crack propagation and coalescence more extensively in the case of a long preexisting fissure. The preexisting fissure angle and two preexisting fissure distances had a negligible effect on the UCS values of the rock-like materials. However, with increasing long preexisting fissure length, the short preexisting fissure was subject to crack propagation and coalescence.

Particle-in-cell techniques for the study of space charge effects in an electrostatic ion beam trap.

We developed a simulation technique to study the effect of space charge interaction between trapped ions in the electrostatic ion beam trap (EIBT). The importance of space charge is demonstrated in both the dispersive and the self-bunching regime of the ion trap. The simulation results provide an estimate for the space charge effect on the trapping efficiency. They also allow for a better understanding of the enhanced diffusion and the self-bunching effect and provide a better characterization of the EIBT as a mass spectrometer, where peak coalescence is important. The numerical results reproduce all experimental data, demonstrating the critical importance of including space charge effects, even at low ion density, to understand the ion trap dynamics.

Unusual complexation behavior between daclatasvir and γ-Cyclodextrin. A multiplatform study.

During a screening of cyclodextrins (CDs) as chiral selectors for the separation of daclatasvir (DCV) and its enantiomer by capillary electrophoresis (CE), an unusual phenomenon for CDs was observed, that is two peaks with a plateau in between using γ-CD as chiral selector. The same result was encountered when enantiopure DCV was injected or when analyzing a sample containing enantiopure DCV and γ-CD in a CD-free background electrolyte. Peak coalescence was observed at 45°C and at a pH above 3.5. Two peaks with a plateau were also observed for DCV stereoisomers as well as a structural analog. However, only a single peak was detected if one or both amino acid moieties of DCV were lacking. Nuclear magnetic resonance (NMR) experiments including Nuclear Overhauser effect-based methods showed that in solution DCV adopted a folded conformation in which the isopropyl side chain of the valine residues pointed toward the aromatic rings of DCV. Moreover, NMR unequivocally demonstrated the simultaneous formation of DCV-γ-CD inclusion complexes with 1:1 and 2:1 stoichiometry, which was corroborated by mass spectrometry. In both complexes, DCV also adopted a folded structure. The RSSR-diastereomer of DCV as well as an analog lacking one of the amino acid moieties also formed 1:1 and 2:1 complexes with γ-CD although a plateau was only observed in the case of the RSSR-diastereomer. As shown by CE-MS, both DCV-γ-CD complexes surprisingly comigrated as the first peak, while the second migrating peak represents non-complexed DCV.

Separation of carbohydrate isomers and anomers on poly-N-(1H-tetrazole-5-yl)-methacrylamide-bonded stationary phase by hydrophilic interaction chromatography as well as determination of anomer interconversion energy barriers

A new commercially available HPLC column, poly-N-(1H-tetrazole-5-yl)-methacrylamide-bonded stationary phase (Daicel DCpak PTZ), was systematically evaluated for its carbohydrate isomer separation capability by hydrophilic interaction liquid chromatography (HILIC) with charged aerosol detection (CAD) or (tandem) mass spectrometry. Reducing sugars tend to split into two anomer peaks which makes carbohydrate isomer separations in non-derivatized form even more complicated. For practical purposes anomer separations are therefore ideally suppressed which can be accomplished by using high temperature or high pH that are both associated with fast interconversion kinetics leading to peak coalescence, or on the other hand by conditions with low chromatographic anomer selectivity. Four major hexoses (glucose, mannose, galactose, fructose), five main pentoses (ribose, ribulose, xylose, xylulose, arabinose) and five most important disaccharides (maltose, cellobiose, lactose, sucrose, trehalose) were analyzed as single carbohydrate standards by isocratic HILIC with 0.1% (v/v) formic acid and 2 mM ammonium acetate at various temperatures to study anomer interconversion equilibria in a pH-dependent manner. Rate constants of forward (α→β) and backward (β→α) anomerization and corresponding energy barriers were calculated. The energy barriers of anomerisation were in the range of around 83–91 kJ mol−1 at 298 K and the difference between forward (α→β) and backward reaction (β→α) was typically between 1–3 kJ mol−1. The systematic studies finally allowed to pick conditions for the simultaneous analysis of all 14 carbohydrates by HILIC-ESI-MS(/MS) with PTZ in gradient elution mode. A combination of carbohydrate isomer-selective LC (with PTZ), tandem MS (with carbohydrate group-selective MS1 and some species-specific SRM transitions) and a simple deconvolution strategy allowed the determination of all carbohydrates of the complex test mixture except for the disaccharide pair lactose and maltose (which can be determined as sum). Consequently, the proposed method represents a successful step towards a global glycometabolomics profiling method of mono- and disaccharides by HILIC-ESI-MS/MS.

Voiding Mechanisms in Deformed Polyamide 6 Observed at the Nanometric Scale

Micromechanisms of deformation and cavitation within the spherulitic microstructure of a polyamide 6 (PA6) material have been observed with a true spatial resolution of 50 nm by magnified synchrotron radiation holotomography. Smooth round bars in PA6 were submitted to interrupted monotonic tensile tests. Before the engineering peak stress, only pre-existing nanometric voids were identified. At the peak stress, void growth and coalescence have been observed in the neck and 2 mm apart from the neck along the revolution axis. Two kinds of cavity arrangements have also been identified, studied quantitatively, and attributed to specific regions of the deformed spherulites. Voiding appeared in the equatorial plane of the spherulites as diffuse annular voided zones, and polar fans were characteristically penny-shaped voids stacked in columns parallel to the loading axis in the spherulite poles. A cylindrical volume located at the center of these spherulites remained intact (no voids).

Utility of Higher Harmonics in Electrospray Ionization Fourier Transform Electrostatic Linear Ion Trap Mass Spectrometry.

Mass resolution (M/ΔM fwhm) is observed to linearly increase with harmonic order in a Fourier transform electrostatic linear ion trap (ELIT) mass spectrometer. This behavior was predicted by Grosshans and Marshall for frequency-multiple detection in a Fourier transform ion cyclotron resonance mass spectrometer only for situations when the prominent mechanism for signal decay is ion ejection from the trap. As the analyzer pressure in our ELIT chamber is relatively high, such that collisional scattering and collision-induced dissociation are expected to underlie much of the ion loss, we sought to explore the relationship between harmonic order and mass resolution. Mass resolutions of 36 900 (fundamental), 75 850 (2nd harmonic), and 108 200 (3rd harmonic) were obtained for GdO+ (avg. m/z 173.919) with a transient length of 300 ms. To demonstrate that the mass resolution was truly increasing with harmonic order, the unresolved isotopes at the fundamental distribution of cytochrome c+8 (m/z ∼ 1549) were nearly baseline, resolved at the third harmonic (mass resolution ≈ 23 000) with a transient length of only 200 ms. This experiment demonstrates that, when the ion density is sufficiently low, ions with frequency differences of less than 4 Hz remain uncoalesced. Higher harmonics can be used to increase the effective mass resolution for a fixed transient length and thereby may enable the resolution of closely spaced masses, determination of a protein ion's charge state, and study of the onset of peak coalescence when the resolution at the fundamental frequency is insufficient.

Numerical study of stress distribution and crack coalescence mechanisms of a solid containing multiple holes

This study investigated the change of stress with crack development, using the numerical code RFPA3D, so as to understand the crack coalescence mechanisms occurring within a heterogeneous solid containing multiple holes loaded in a state of uniaxial compression. A full discussion is presented on a statistical analysis of observed microcracks data, and on the appropriate parameter selection based on those microcrack statistics. The simulated peak stress results and coalescence patterns using the selected parameters were found to closely resemble previous experimental observations. A full investigation and discussion of the stress distributions around holes during the crack growth and coalescence processes is presented for heterogeneous sample cases. Under applied loading, crack initiation, growth direction and coalescence pattern are strongly influenced by the shape of the interaction tensile zone formed between holes. Acoustic emission (AE) analysis in relation to the numerical simulations indicates that no case of pure tensile crack coalescence occurs between holes. Three modes of coalescence are classified: Ts mode (tensile mode coalescence with shear), MT mode (mixed mode coalescence with tensile mode dominant) and M mode (mixed mode coalescence). The crack coalescence mechanisms and patterns were further investigated by changing the parameters of normalized bridge length (d/r), bridge angle β and number of holes. A precise crack coalescence criterion is proposed.

Electron Dynamics and IR Peak Coalescence in Bridged Mixed Valence Dimers Studied by Ultrafast 2D-IR Spectroscopy.

Dynamic IR peak coalescence and simulations based on the optical Bloch equations have been used previously to predict the rates of intramolecular electron transfer in a group of bridged mixed valence dimers of the type [Ru3(O)(OAc)6(CO)L]-BL-[Ru3(O) (OAc)6(CO)L]. However, limitations of the Bloch equations for the analysis of dynamical coalescence in vibrational spectra have been described. We have used ultrafast 2D-IR spectroscopy to investigate the vibrational dynamics of the CO spectator ligands of several dimers in the group. These experiments reveal that no electron site exchange occurs on the time scale required to explain the observed peak coalescence. The high variability in FTIR peak shapes for these mixed valence systems is suggested to be the result of fluctuations in the charge distributions at each metal cluster within a single-well potential energy surface, rather than the previous model of two-site exchange.

Twelve Million Resolving Power on 4.7 T Fourier Transform Ion Cyclotron Resonance Instrument with Dynamically Harmonized Cell—Observation of Fine Structure in Peptide Mass Spectra

Resolving power of about 12,000 000 at m/z 675 has been achieved on low field homogeneity 4.7T magnet using a dynamically harmonized Fourier transform ion cyclotron resonance (FT ICR) cell. Mass spectra of the fine structure of the isotopic distribution of a peptide were obtained and strong discrimination of small intensity peaks was observed in case of resonance excitation of the ions of the whole isotopic cluster to the same cyclotron radius. The absence of some peaks from the mass spectra of the fine structure was explained basing on results of computer simulations showing strong ion cloud interactions, which cause the coalescence of peaks with m/z close to that of the highest magnitude peak. The way to prevent peak discrimination is to excite ion clouds of different m/z to different cyclotron radii, which was demonstrated and investigated both experimentally and by computer simulations.

High sensitivity Polyvinylidene Fluoride (PVDF) microphone based on area ratio amplification and minimal capacitance

This paper presents an inexpensive high-sensitivity microphone based on polyvinylidene fluoride (PVDF) film. High sensitivity is achieved through pressure amplification created by the area ratio between the rigid surface exposed to acoustic waves and a crosshair-shaped PVDF film, in combination with the reduced capacitance created by a similarly shaped top electrode. The crosshair shape is obtained through simple chemical etching from commercial PVDF film. Finite-element simulations including static structure analysis, modal analysis, and harmonic response are performed to design the microphone. Peak coalescence of the first three adjacent natural frequencies caused by the structure damping ratio is observed. Static and dynamic stress analyses ensure that the design meets the mechanical constraints imposed by PVDF. A plane wave tube experiment and signal conditioning electronics are developed. Measurements include benchmarking against a commercial microphone and show that the PVDF microphone exhibits a linear response up to a sound pressure level of 140 dB and overall fluctuations of less than ±4 dB over the frequency range of 10 to 20000 Hz. The sensitivity of the microphone alone, without a conditioning circuit, is measured as 27.8 μV/Pa, which is 3.01 times the sensitivity of commercial PVDF film operating in 3-3 mode. This sensitivity gain is close to the physical area ratio of 3.2. We experimentally characterize the directivity of the sensor and measure a decay of -10.5 dB at ±90° from the microphone's axis.

Application of cinchona-sulfonate-based chiral zwitterionic ion exchangers for the separation of proline-containing dipeptide rotamers and determination of on-column isomerization parameters from dynamic elution profiles

The interconversion of cis and trans isomers of dipeptides containing C-terminal proline was studied by dynamic chromatography on zwitterionic chiral stationary phases at temperatures ranging from −15°C to +45°C The cis–trans isomers could be separated below 0°C and above 0–10°C plateau formation and peak coalescence phenomena occurred, which is characteristic for a dynamic process at the time-scale of partitioning. At and above room temperature, full coalescence was observed, which allowed separations of enantiomers without interference from interconversion effects. Analysis of the dynamic elution profiles of the interconverting peptides allowed the determination of isomerization rate constants and thermodynamic activation parameters (isomerization enthalpy, entropy and activation energy). In accordance with established results, isomerization rates and thermodynamic parameters were found to depend on the nature of the N-terminal amino acid. Isomerization barriers were only slightly lower than values determined with other methods but significant differences in the relative contributions of the activation enthalpy and entropy as well as isomerization rates pointed toward selector-moderated isomerization dynamics.

Accelerated Simulation Study of Space Charge Effects in Quadrupole Ion Traps Using GPU Techniques

Space charge effects play important roles in the performance of various types of mass analyzers. Simulation of space charge effects is often limited by the computation capability. In this study, we evaluate the method of using graphics processing unit (GPU) to accelerate ion trajectory simulation. Simulation using GPU has been compared with multi-core central processing unit (CPU), and an acceleration of about 390 times have been obtained using a single computer for simulation of up to 10(5) ions in quadrupole ion traps. Characteristics of trapped ions can be investigated at detailed levels within a reasonable simulation time. Space charge effects on the trapping capacities of linear and 3D ion traps, ion cloud shapes, ion motion frequency shift, mass spectrum peak coalescence effects between two ion clouds of close m/z are studied with the ion trajectory simulation using GPU.

Fourier Transform Ion Cyclotron Resonance Mass Resolution and Dynamic Range Limits Calculated by Computer Modeling of Ion Cloud Motion

Particle-in-Cell (PIC) ion trajectory calculations provide the most realistic simulation of Fourier transform ion cyclotron resonance (FT-ICR) experiments by efficient and accurate calculation of the forces acting on each ion in an ensemble (cloud), including Coulomb interactions (space charge), the electric field of the ICR trap electrodes, image charges on the trap electrodes, the magnetic field, and collisions with neutral gas molecules. It has been shown recently that ion cloud collective behavior is required to generate an FT-ICR signal and that two main phenomena influence mass resolution and dynamic range. The first is formation of an ellipsoidal ion cloud (termed "condensation") at a critical ion number (density), which facilitates signal generation in an FT-ICR cell of arbitrary geometry because the condensed cloud behaves as a quasi-ion. The second phenomenon is peak coalescence. Ion resonances that are closely spaced in m/z coalesce into one resonance if the ion number (density) exceeds a threshold that depends on magnetic field strength, ion cyclotron radius, ion masses and mass difference, and ion initial spatial distribution. These two phenomena decrease dynamic range by rapid cloud dephasing at small ion density and by cloud coalescence at high ion density. Here, we use PIC simulations to quantitate the dependence of coalescence on each critical parameter. Transitions between independent and coalesced motion were observed in a series of the experiments that systematically varied ion number, magnetic field strength, ion radius, ion m/z, ion m/z difference, and ion initial spatial distribution (the present simulations begin from elliptically-shaped ion clouds with constant ion density distribution). Our simulations show that mass resolution is constant at a given magnetic field strength with increasing ion number until a critical value (N) is reached. N dependence on magnetic field strength, cyclotron radius, ion mass, and difference between ion masses was determined for two ion ensembles of different m/z, equal abundance, and equal cyclotron radius. We find that N and dynamic range depend quadratically on magnetic field strength in the range 1-21 Tesla. Dependences on cyclotron radius and Δm/z are linear. N depends on m/z as (m/z)(-2). Empirical expressions for mass resolution as a function of each of the experimental parameters are presented. Here, we provide the first exposition of the origin and extent of trade-off between FT-ICR MS dynamic range and mass resolution (defined not as line width, but as the separation between the most closely resolved masses).

Unit mass baseline resolution for an intact 148 kDa therapeutic monoclonal antibody by Fourier transform ion cyclotron resonance mass spectrometry.

Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) provides the highest mass resolving power and mass measurement accuracy for unambiguous identification of biomolecules. Previously, the highest-mass protein for which FTICR unit mass resolution had been obtained was 115 kDa at 7 T. Here, we present baseline resolution for an intact 147.7 kDa monoclonal antibody (mAb), by prior dissociation of noncovalent adducts, optimization of detected total ion number, and optimization of ICR cell parameters to minimize space charge shifts, peak coalescence, and destructive ion cloud Coulombic interactions. The resultant long ICR transient lifetime (as high as 20 s) results in magnitude-mode mass resolving power of ~420,000 at m/z 2,593 for the 57+ charge state (the highest mass for which baseline unit mass resolution has been achieved), auguring for future characterization of even larger intact proteins and protein complexes by FTICR MS. We also demonstrate up to 80% higher resolving power by phase correction to yield an absorption-mode mass spectrum.