bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving the Accuracy of Machined Parametric Surfaces Using Cutting Force Synthesis and Surface Offset Techniques
Authors: Gadalla Mohamed A. E. , ElMaraghy Waguih H.
Published: March 2022

Prediction of machining errors and compensation for these errors during the tool path generation stage can improve the product quality significantly. A traditional approach would be machining a few parts, followed by a measuring process to estimate the errors, and finally using a scheme to compensate for the errors. In this paper two approaches are used to avoid trial runs. In the first approach prediction of the deflection of the cutting tool (based on modelling of the cutting forces) at certain points distributed on the design surface is calculated. An inverse operator is then applied to these errors to calculate a compensation vector at each point. A variable offset geometrical model was developed that uses these vectors to build the compensated surface. A detailed simulation analysis for the proposed compensation scheme is presented for different surface shapes in both up and down milling. The second approach is based on improving the roughing strategy by leaving a uniform thickness layer during the roughing phase on top of the finished surface. This leads to more uniform distribution of the cutting forces that may improve the accuracy of the finished surface.
Experimental Study of the Pre-Stressing Capability Through Residual Stress Generation in Superfinish Machining of Hardened Steel
Authors: Liu C. R. , Agha S. R.
Published: March 2022

It has been recently shown, [Liu and Mittal 1995, 1996] that it is feasible to eliminate the needs for grinding and superfinishing by turning, in selected conditions, directly on hardened steel up to a hardness of 64 RC, for a surface finish of Ra smaller than 8 μ in. Furthermore, it was shown that hard turning is capable of pre-stressing the machined surface so that it may partially “compensate” the surface load for improved fatigue life. A preliminary study has indicated a potential improvement of over 200% in fatigue life is possible. It also offers a prospect that it is possible to produce a component which will never fail due to fatigue. Therefore, it is desirable to explore the capability of pre-stressing by finish hard turning in broad machining condition, thus this study. The purpose of this study is to investigate the residual stress after finish machining of hardened AISI 52100 steel with hardness of 60–62 HRC using CBN inserts. The effect of tool, feed rate, and depth of cut on the residual stress distribution are studied. Surface finish better than 8 μ in. was produced comparable to that produced by grinding and superfinishing. The round tool (0.5 inch radius) was found to give more compressive stress than the 0.0623 inch nose radius diamond-shaped tool. The smaller feed rate gave more compressive residual stress.
A Dynamic Model for Bound Abrasive Grinding of Optical Materials: The Effect of Grinding Conditions on the Workpiece Surface Quality
Authors: Takahashi Toshio , Funkenbusch Paul D.
Published: March 2022

A simple dynamic model to describe the grinding behavior in bound abrasive microgrinding of optical materials with CNC (Computerized Numerical Control) machining equipment is discussed and compared with data collected from direct measurement of grinding force. The model involves the relation between grinding force and material removal rate, machine stiffness, and tool condition. Measurements have shown that the tool’s effectiveness and the workpiece surface quality are closely tied through the normal load exerted by the tool on the workpiece during grinding.
A Neural Network Based Interactive Programing of a Deburring Robot in a Virtual Environment
Authors: Kesavadas T. , Khor Chin
Published: March 2022

This paper describes an interactive neural network based system for specifying robotic tasks using virtual tools. This virtual environment allows an operator to reach into a live video scene and direct robots to use corresponding real tools to carry out complex metal finishing tasks. The virtual tool concept provides a human-machine interface that is robust to unanticipated developments and tunable to the specific requirements of a particular task. This interactive specification concept is applied to robotic deburring processes. A function is formulated to map the end-effector position of this robot to corresponding set of joint angles through a neural network learning process obtained through examples. The experimental result of such a system that has been implemented on the Mitsubishi RV-M1 robot shows the efficiency of the approach and its potential for use in virtual reality based interactive robotics.
Preview Control for Robot Force Control: Experimental Investigation of Edge-Following
Authors: Yong Boojoong
Published: March 2022

It is often useful in automation tasks to make a robot manipulator interact with its environment in a controlled manner. This paper considers an edge-following using accommodation force control. The robot behavior changes with configuration, and unexpected workpiece disturbances degrade the system performance. The tracking speed and force regulation of the edge-following can be improved by preview control. The preview controller is implemented on an industrial robot system, and experiments are carried out to verify validity of the preview control.
Striation Formation and Surface Finish in Laser Cutting of Mild Steel
Authors: Chen Kai , Yao Y. Lawrence
Published: March 2022

The mechanisms of melt ejection and striation formation in laser cutting of mild steel are discussed. It is argued that the melt ejection from the cutting front is not a steady state process, but rather shows a cyclic phenomenon. The striation are strongly affected by the unstable characteristic of the thin liquid film on the cutting front during the melt ejection, together with the oxidation and heat transfer process. Dependent on the cutting speed, the liquid film will either rupture or generate waves on the cutting front. Theoretical explanation is given according to the instability theory of a thin liquid film in a high velocity gas jet and the diffusion controlled oxidation theory. The striation frequency and depth can be estimated according to the above theories. Experimental investigations were carried out and the results are consistent with the calculations. The better understanding has shed light on further investigations and optimal process development.
Discharge Quality Estimation and Significant Feature Identification in Micro-Electrical Discharge Machining
Authors: Ramabhadran R. , Hebbar R. R. , Kashyap R. L. , Chandrasekar S.
Published: March 2022

We present a method for estimating the quality of a measured discharge train in Micro-EDM processes. In contrast to generic EDM, Micro-EDM is characterized by a higher frequency of discharges and is used for machining smaller features, thus making regulation more difficult. In this paper, a system similar to a fuzzy rule based classification is used to identify good and bad disharges based on discharge quality. In addition to traditional machining quality issues, we include parameters that illustrate the degree of control of the voltage pulse input over the spark gap. To aid the formulation of quick closed loop control schemes for Micro-EDM, a method for identifying the parameter/sensor that separates best the good and bad discharges, is presented. The use of this method in closed loop control schemes for Micro-EDM is discussed.
Transient and Steady-State Thermal Design Evaluation of a Carbon Monoxide Gas Sensor Using CFD Tool
Authors: Lee Tien-Yu Tom , Sharma Ravi , Peyre-Lavigne André
Published: March 2022

This paper summarizes thermal modeling work performed on the Motorola Carbon Monoxide (CO) chemical sensor. Gas sensors need low cost reliable packages, good thermal operation, and low power consumption. The goal is to provide a validated thermal model of a gas sensor and its package and develop a sensor design capability with reduced design cycle time. Due to the complex structure of the sensor package, Computational Fluid Dynamics (CFD) tool was used to analyze the heat transfer and fluid flow within the package. Based on the validated model, parametric studies on filter location and package orientation were performed. In order to minimize the influence of humidity, the sensor is toggled between high and low temperatures by applying 5 volts for 5 seconds of heating, and 1 volt for 10 seconds of cooling. Transient thermal analysis was also performed to predict the temperature response of various components. A detailed description of the thermal model and its results are described in the paper.
On the Equivalent Finite Element Beam Model for Ball Grid Array Analysis
Authors: Cheng Hsien-Chie , Chiang Kuo-Ning , Lee Ming-Hsiao
Published: March 2022

Literaturally, the local-global finite element analysis technique plays a very important role in the area array packaging. This technique applies a finite element based method to calculate the geometrical data and elastic/plastic material properties of the equivalent beam model that is used to elastically and plastically simulate the 3-D local model. In this study, the underlying goal is to propose an improved equivalent model for the use in the local/global analysis, and most importantly, provide a systematic procedure in approaching this equivalent model. In addition, the choice of the equivalent beam model (i.e., either solid circular beam or the thin-walled circular pipe) will be also extensively investigated. Since the configuration of the solder joint is far from being close to a “beam-like” structure, defining the corresponding equivalent beam exists a great level of difficulties. Hence, in order to remove the possible difficulties, a comparatively effective way is proposed by incorporating the analytical derivations and optimization approaches. To this end, one practical application is presented to substantiate the proposed methodology.
Sequential Processing Mechanics Modeling for a Model IC Package
Authors: Wang Jianjun , Liu Sheng
Published: March 2022

In this paper, a non-linear finite element framework was established for processing mechanics modeling of electronic packaging assemblies and layered manufacturing. In particular, topological change was considered in order to model the sequential steps during a typical IC package assembly. Geometric and material nonlinearity, temperature-dependent material properties were considered. Different stress-free temperatures for different elements in the same model were used to simulate practical manufacturing process-induced thermal residual stress field in the chip assembly. As comparison, two FEM models (Processing Model and Non-Processing Model) of a encapsulated IC package considered, associated with different processing schemes, were analyzed. From the finite element analysis, it is found that due to the coefficient of thermal expansion (CTE) mismatch between the solder and silicon chip, the substrate and the solder, there exist very high stress fields near these interfaces when the encapsulated IC package is cooled down to room temperature after processing for these two models. But in contrast with the stresses near the edges of all interfaces obtained from Non-Processing Model, the stresses near the edges of all interfaces corresponding to Processing Model are generally higher than those obtained from Non-Processing Model. In particular, the Von Mises stress at the edge of silicon chip/solder interface obtained from Processing Model is nearly 50% higher than that obtained from Non-Processing Model. It is shown that Processing Model which is based on the FEM framework established in this paper can more realistically simulate a series of practical manufacturing processes in the chip assembly, whereas a larger error can be caused by using Non-Processing Model in the analysis of process-induced residual stress field in the packaging assemblies due to the negligence of the bonding process during cooling from 250° C to 160° C.
A Review of Changes and Trends Affecting Military Electronics Manufacturing
Authors: Rafanelli Anthony J.
Published: March 2022

Dramatic business changes in the aerospace and military defense industries have caused contractors to drastically alter their design and manufacturing processes. These changes appear to have been influenced by recent events or movements: The U.S. Department of Defense initiative (Perry, 1994 and U.S. DoD, 9 December 1994) discourage dependence on military specifications/standards (the “Perry Initiative”) which resulted in trends within the electronics industry to use commercial materials in typical military environments (alternative component initiatives). Consequently, changes are underway regarding some of the traditional technologies used in defense electronics. Specifically, this paper will present an overview of the changing nature of some of these technologies, e.g. interconnections, coatings, and plastic encapsulated microcircuits (PEMs) and the standards/practices related to these from a manufacturing aspect. The information, provided, is by no means all-inclusive, but does identify a focus for increased discussion and study.
A Slip-Line Field for Ploughing During Orthogonal Cutting
Authors: Waldorf Daniel J. , DeVor Richard E. , Kapoor Shiv G.
Published: March 2022

Under normal machining conditions, the cutting forces are primarily due to the bulk shearing of the workpiece material in a narrow zone called the shear zone. However, under finishing conditions, when the uncut chip thickness is of the order of the cutting edge radius, a ploughing component of the forces becomes significant as compared to the shear forces. Predicting forces under these conditions requires an estimate of ploughing. A slip-line field is developed to model the ploughing components of the cutting force. The field is based on other slip-line fields developed for a rigid wedge sliding on a half-space and for negative rake angle orthogonal cutting. It incorporates the observed phenomena of a small stable build-up of material adhered to the edge and a raised prow of material formed ahead of the edge. The model shows how ploughing forces are related to cutter edge radius — a larger edge causing larger ploughing forces. A series of experiments were run on 6061-T6 aluminum using tools with different edge radii — including some exaggerated in size – and different levels of uncut chip thickness. Resulting force measurements match well to predictions using the proposed slip-line field. The results show great promise for understanding and quantifying the effects of edge radius and worn tool on cutting forces.
A Structured Approach to Analytical Multi-Degree-of-Freedom Time-Invariant Stability Analysis for Machining
Authors: Ozdoganlar O. Burak , Endres William J.
Published: March 2022

A general, fully analytical stability solution for multi-degree-of-freedom machining is derived based on the formulation of an eigenvalue problem. The structure and process are assumed to be linear and time-invariant. A specific-energy-based cutting process model, which has been adopted by many researchers and practitioners, is used here to represent the process. This model is attractive for industrial application since it requires minimal experimentation for its application over a wide range of cutting conditions and tool geometry. The analysis permits arbitrary orientation of the structure’s orthogonal modes relative to the coordinates in which the cutting process is modeled. The final solution differs from others in that the analytical methods are carried through to the final result without need for the numerical methods used by other investigators when applying Nyquist-based analysis for more degrees of freedom than one. This final result for limiting width of cut and chatter phase, being in analytical form, clearly shows the effects of each individual mode on the stability behavior. En route to the multi-degree-of-freedom solution, one- and two-degree-of-freedom cases are addressed to demonstrate the approach.
An Experimental Study of the Effects of Fixture and Workpiece Variables on Workpiece-Fixture Contact Forces in End Milling
Authors: Hurtado Jose F. , Melkote Shreyes N.
Published: March 2022

Contact forces play an important role in restraining workpiece motion during machining. In particular, frictional forces are often used to immobilize the workpiece against machining forces. This paper presents results of an experimental study of the effects of fixture, workpiece, and machining condition variables on workpiece-fixture contact forces in end milling. The effects of locator tip geometry, workpiece stiffness, workpiece surface roughness, and tool feedrate on the normal and tangential forces measured at a workpiece-fixture contact were analyzed statistically. It was found that the interaction of contact geometry and surface roughness has a significant effect on the tangential contact force. The normal contact force was found to be affected mostly by the machining condition and to a lesser extent by the workpiece stiffness. Experiments also suggest that the workpiece-fixture contact friction is considerably influenced by the cyclical nature of the milling forces.
Finite Element Based Fixture Analysis Model for Surface Error Predictions due to Clamping and Machining Forces
Authors: Chandra Prakash , Athavale Shounak M. , Kapoor Shiv G. , DeVor Richard E.
Published: March 2022

A finite element model to analyze effect of clamping sequence, clamping pre-loads and machining loads (forces) on the surface error for face-milled workpieces was developed. A compliant test part was used to test and demonstrate the predictive capabilities of the model. Experimental measurements of surface deflections/errors after clamping, and after machining were compared with the finite element predictions. Both predicted peak-to-valley surface error values and surface error patterns for ZXY clamping sequence were in good agreement with the experimental measurements.

The effects of fixture compliance, workpiece-fixture contact geometry (point / area contact), and clamping preloads on the surface error predictions were also studied. The clamping preloads have the most significant impact on the surface error during fixturing of flexible parts, followed by effect of contact area geometry. Fixture compliance, however, does not significantly affect the surface error in case of structurally compliant parts.
Mechanistic Force Models for Chip Control Tools
Authors: Zhu Rixin , Athavale Shounak M. , Kapoor Shiv G. , DeVor Richard E.
Published: March 2022

A mechanistic modeling approach to predicting machining forces for grooved tools is developed. The models are solely based on the grooved tool geometry and the specific cutting energy and friction energy for flat tools. Special grooved tools (M2 grade HSS) were designed and fabricated and orthogonal cutting tests were performed to validate the model. The workpiece material used was Al 6061-T6. The force predictions from the model are found in good agreement with the measured forces. The effects of groove design parameters on the cutting forces are also determined.
Influence of the Clamping Mechanism on Tool Failure During Dry High Speed Machining
Authors: El-Wardany Tahany I. , Elbestawi Mohamed A.
Published: March 2022

This paper studies the effect of the clamping conditions on the brittle fracture of the poly-crystalline cubic boron nitride (PCBN) insert during dry high speed machining of gray cast iron. Dry high speed face turning tests are performed on a composite design disc brake rotor to investigate the brittle fracture of the PCBN insert. Scanning electron microscopic analysis is used to examine the fractured surface. A thermo-elasto-plastic finite element analysis is employed to determine the stresses induced in the insert due to thermal and mechanical loading generated during cutting. Different clamping conditions, tool holder materials and clamping torques are considered. The analysis reveals that a steeper temperature drop on the PCBN tool rake face results when a carbide chip breaker is used between the clamp and the insert and also when a Mallory 100 M or Aluminum tool holders are used. As a result high thermal stresses are obtained on the insert rake face. The brittle fracture of the insert is originated at the rake face at a local maximum of tensile stress. The results also indicate that reducing the clamping torque and or removing the chip breaker reduces the local maximum tensile stresses on the rake face and increases the tool life by tenfold.
Performance Analysis of Parallel Manipulator Architectures for CNC Machining Applications
Authors: Kim Jin Wook , Park Changbeom , Kim Jongwon , Park F. C.
Published: March 2022

Parallel manipulators of the Stewart-Gough Platform type have been receiving increasing attention as mechanical platforms for universal machining centers. In this paper we investigate the performance of various parallel manipulator architectures for CNC machining applications. The kinematic characeristics that are most often cited as important in universal machining include qualities like manipulability, joint and link stiffness, and workspace volume. Here we quantify these various performance measures using differential geometric techniques, and investigate the performance of two six degree-of-freedom parallel manipulators which have been built as commercial products or research prototypes. The analytical methodology presented here, in combination with the graphics-based CAD software we have developed, can serve as a useful tool to designers of future high-performance parallel manipulator-based machine tools.
Stability Analysis in Face Milling Operations: Part 2 — Experimental Validation and Influencing Factors
Authors: Jensen Steve A. , Shin Yung C.
Published: March 2022

This paper presents the rigorous experimental validation results of the stability algorithm as developed in the part 1. The two experiments which will be presented here focus on; first, a workpiece whose vibrational modes constitute the weakest part of the overall system, and second, a machine tool whose vibrational modes are the weakest part of the system. Next, it discusses some of the influencing factors that affect the on-set of chatter in face milling processes. The factors considered include cutting conditions, entry and exit angles, axial dynamics, cutter geometry, material properties and structural dynamic parameters. Lastly, it presents the effect of structural dynamic change under operating condition on stability lobes.
Forward and Inverse Kinematic Solutions of a New Three Dimensional Metrology Frame
Authors: Schinstock Dale E. , Cuttino James F.
Published: March 2022

A concept for a three dimensional, non-contacting metrology system is presented. Both the forward and the inverse kinematics solutions for the system are developed using a line geometry, resulting in an efficient representation that may describe a general assembly of the kinematic system and error parameters determined through calibration. The inverse kinematics solution is a general solution, assuming very little about the assembly of the system. The forward kinematics solution is less general and resorts to making a few assumptions. In the development of the forward and inverse kinematics solutions singularities of the system are identified.
High-Speed Scanning of Piezo-Probes for Nano-Fabrication
Authors: Croft Donald , McAllister David , Devasia Santosh
Published: March 2022

Low scanning speed of piezo-probes has been a fundamental limitation of scanning probe based nano-fabrication techniques. Typical scan-rates achieved are limited, by structural vibrations of the piezo-probe, to about 1/10th the fundamental vibrational frequency of the piezo-probe. Faster scanning of piezo-probes is achieved here (experimental results are presented) by using inversion of the piezo-dynamics — this approach uses a feedforward input voltage, applied to piezo-probe, to compensate for piezo vibrations.
Improving Electronic Packaging Manufacturing Through Product and Process-Driven Analysis: A PWB Case Study
Authors: Scholand Andrew J. , Peak Russell S. , Fulton Robert E.
Published: March 2022

This paper demonstrates how the use of product analysis combined with process data can provide information about the product quality impact of high-level process decisions. A specific case study involving the warpage of two PWB designs as they move through a reflow oven is presented. A new approximate thermal model is derived which analyzes processing rate dependent warpage, an important metric of product quality for ovens with edge support conveyance systems. Agreement between the theoretical model and prior published experimental results was found to be strongly dependent on the precise temperature dependent material property values used, underlining the need to have accurate thermo-mechanical characterizations of PWB constituent materials. A set of property values based on data published in the literature was assembled which provided a fair match to experimental results, giving sufficient confidence to apply the model predictively. For the case study presented, the model predicts a 10% decrease in processing time will increase board warpage by at most 11.5%. This case study illustrates how product analysis can arm production managers with the information they need to make informed, effective decisions which trade off the economic gains realizable by implementing process improvements against the product quality impact of those improvements.
In Process Stress Analysis of Flip Chip Assemblies During Underfill Cure
Authors: Palaniappan Prema , Baldwin Daniel F.
Published: March 2022

The electronics industry is currently evaluating flip chip technology for high performance, miniaturized assembly applications. This is primarily because of the high I/O density, small form factor, and superior electrical performance provided by flip chip on board technology. Flip chip on low cost circuit boards (FCOB) furnishes a reliable interconnection provided underfill materials are used. Underfills overcome the thermomechanical reliability issues associated with the thermal expansion coefficient mismatch between the board and die. The selection of underfill material is critical to achieving the desired performance and reliability. Processing of underfills during assembly can result in large residual stresses within the silicon die. In some instances these stresses can be large enough to cause die fracture.

In this work, low cost flip chip on board assemblies are analyzed during the underfill cure process. In situ stress measurements are performed over the active face of the die during processing and relative in-plane stresses are measured. Experimental measurements are made using flip chip test vehicles based on Sandia National Laboratories’ ATC04 Assembly Test Chip. Four different commercial underfill materials have been evaluated and a relative comparison is presented. Significant stress variations are observed between the four underfills studied. Correlation’s between the glass transition temperature (Tg) and storage modulus (G’) are made relative to residual stresses produced during underfill cure.
Accelerated Reliability Testing Method for Sensors With a Pulsing Membrane Structure
Authors: Guo Yifan , Sarihan Vijay , Lee Tom
Published: March 2022

In chemical sensors, the sensing element is heated to a high temperature (around 450°C) for optimizing sensitivity and selectivity. In order to minimize power dissipation, the power supply for the heating is operated in a pulsed mode. The duration of the high temperature period is set by the required sensor response time for low gas concentrations. In qualification of chemical sensors, it is important to test the reliability of the membrane structures under realistic conditions of pulsed-mode operation. From these data, it is possible to link time-to-failure with changes in material or layout design. Under the operation condition, the cyclic power input generates local heat and thermal gradient in the membrane as well as physical deformation and local stress. The regular reliability test — thermal cycles with isothermal temperature distribution — cannot simulate the membrane stress or induce the failure processes that occur in the membrane, heater or sensor films under real operational conditions. This paper describes a unique testing technique which is suited for reliability tests and field life prediction in a pulsed sensor. The methods of determining the acceleration factor and the procedures to execute the life test are discussed. Using this testing method, the fatigue life of the sensor configurations can be evaluated within a much shortened testing time.
A Window Based Graphics Interface for Phase Shifting Analysis in Moire Interferometry
Authors: He Xiaoyuan , Zou Daqing , Liu Sheng , Guo Yifan
Published: March 2022

A window based graphics interface for phase shifting in a moiré interferometry system is introduced in this paper. VISUAL C++ is used in the software programming. The phase shifting is accomplished by driving the reference grating in the moiré interfermetry system with a low voltage piezo stack. Four images from three shifts and one original image are used to derive the phase diagram, which is used for displacement and strain calculations. Automatic fringe numbering is achieved by the phase shifting, which significantly simplifies the traditional fringe-counting process. The strain calculation is also automatic by space derivative of displacement. The displacement distribution is obtained by unwrapping the phase diagram. Various help menu functions are provided, facilitating the ease use of the software. A 3-point bending beam is used for the demonstration. The technique is also applied to the analysis of thermal deformations in a flip-chip electronic package.
The MicroDAC Method: A Powerful Means for Microdeformation Analysis in Electronic Packaging
Authors: Michel Bernd , Vogel Dietmar , Schubert Andreas , Auersperg Jürgen , Reichl Herbert
Published: March 2022

Besides different accelerated testing methods finite element analysis (FEA) of stressed components together with appropriate failure hypothesizes allow to estimate life time characteristics. However, most of structures of interest are rather complex and often all necessary material laws or parameters are not available. For simplified simulations the problem arises, whether the results describe adequately the real component under stress. MicroDAC — an established versatile approach to measurement of displacement and strain fields on thermally or mechanically stressed specimens can help to overcome the problem. The underlying measurement principle is a correlation based computer algorithm. It allows to track a set of local object pattern on optical or scanning electron micrographs for different load conditions. The resultant displacement and strain fields are being compared with finite element analysis (FEA) findings or used as an independent source of data. The measurement method has been applied mainly to solder interconnects at flip chip assemblies and chip scale packages.
Nonlinear Spin-Up of a Rotating Stratified Fluid: Experimental Method and Preliminary Results
Authors: Hewitt Richard E. , Davis Peter A. , Duck Peter W. , Foster Michael R. , Smith Fraser W.
Published: March 2022

We consider the nonlinear spin-up of a rotating stratified fluid in a conical container. An analysis of similarity-type solutions to the relevant boundary-layer problem (Duck, Foster & Hewitt, 1997) has revealed three types of behaviour for this geometry. In general, the boundary-layer evolves to either a steady state, a growing boundary-layer, or a finite-time singularity depending on the initial to final rotation rate ratio, and a “modified Burger number”.

We emphasise the experimental aspects of our continuing spin-up investigations and make some preliminary comparisons with the boundary-layer theory, showing good agreement. The experimental data presented is obtained through particle tracking velocimetry. We briefly discuss the qualitative features of the spin-down experiments which, in general, are dominated by non-axisymmetric effects.

The experiments are performed using a conical container filled with a linearly stratified fluid, the generation of which is non-trivial. We present a general method for creating a linear density profile in containers with sloping boundaries.
Flow Structure in a Rayleigh-Bénard Cell Upon Impulsive Spin-Up
Authors: Vorobieff Peter , Ecke Robert E.
Published: March 2022

We investigate convection in a cylindrical Rayleigh-Bénard cell with radius-to-height ratio Γ = 1/2. The cell is subjected to impulsive spin-up about its vertical axis. We use TLC (thermochromic liquid crystal) for temperature field measurements and PIV (particle image velocimetry) for the velocity reconstruction of the transition in the range of Rayleigh numbers R from 5 × 107 to 5 × 108 and dimensionless rotation rates Ω from 0 up to 8 × 104. The initial (at rest) and the final (in steady rotation) states of the system are those of turbulent convection. The most persistent transient feature is a sharply defined ringlike pattern characterized by a decrease in temperature, axial velocity directed downward and high azimuthal shear. The latter leads to formation of an azimuthally regular structure of Kelvin-Helmholz vortices. During the final stage of the transition, this vortical structure loses azimuthal regularity and an irregular pattern of vortices characteristic of turbulent rotating convection forms.
Transient Character of Positively and Negatively Buoyant Turbulent Jets
Authors: Pantzlaff Lars , Lueptow Richard M.
Published: March 2022

The transient character of the jet issuing from an upward nozzle centered in the bottom of a vertical cylindrical tank into bulk liquid of a different density was measured for varying jet Reynolds numbers and ratios of fluid densities using flow visualization and PIV. Positively buoyant jets penetrate to the free surface, driven by both momentum and buoyancy in the upward direction. The lighter jet fluid stratifies in a layer above the bulk liquid. Upon starting, a negatively buoyant jet has three stages. First the jet penetrates to its maximum height in the tank. Then the jet penetration decreases due to the downward backflow of heavier fluid surrounding the jet, which reduces the jet’s upward momentum. Finally the jet penetration height fluctuates around a mean value about 70% the maximum height of penetration. For small negative densimetric Froude numbers (−6075 ≤ Fr ≤ −250), the flow is fountain-like. The downward flow turns radially outward as it reaches the bottom of the tank and eventually an annular recirculation zone forms at the bottom of the tank with vortical motion opposite the vorticity of the inflowing jet. For large negative Froude numbers (Fr ≤ −7770), the spreading of the jet extends far enough so the annular downward flow is along the walls of the tank resulting in a large annular recirculation zone. Scaling the jet penetration and time with the buoyancy flux and the jet momentum flux results in collapse of the transient jet penetration over a wide range of Froude numbers.
Cavitation Predictions Using a Panel Method
Authors: Mueller A. C. , Kinnas S. A.
Published: March 2022

A boundary element method is used to predict the time-dependent cavitation on a propeller subject to non-axisymmetric inflow. The convergence of the method is studied. The predicted cavities agree well with those observed in CAPREX, an experiment performed at MIT’s variable pressure water tunnel. The method is modified so that prediction of cavities detaching at mid-chord regions is possible. An algorithm for predicting the cavity detachment location on the blade is described and applied on a blade geometry which exhibits mid-chord cavitation.
Wave-Generated Forces and Moments on Submersibles: Models for Dynamic Simulation at Periscope Depth
Authors: Chhabra Narender K. , Scholten James R. , Lozow Jeffrey B.
Published: March 2022

Analysis of the wave-induced motion of underwater vehicles near the ocean surface is a difficult task. First, the action of the fluid must be decomposed into ideal (inviscid) and real (viscous) effects. Next, each effect must be modeled as to its interaction with the submerged body. The effect of the body on the waves must be considered. In shallow water, the ocean bottom has many effects: energy-dissipation tends to reduce wave height; land-proximity restricts the wave direction; and the bottom boundary changes the shape of the waves, attenuating the vertical (but not the horizontal) component of motion. This paper presents mathematical models for predicting realistic wave-generated forces and moments on submersible vehicles. Included are models which generate typical wave spectra for deep and shallow waters, models for wave kinematics as affected by flat or sloping bottoms, and models for forces and moments on submersibles due to these surface waves.

Forces and moments are computed using two alternative methods. One is a fast method based on analytical integration of dynamic pressure forces over the surface of an elongated ellipsoidal body. It gives first-order forces and moments limited to horizontal and restrained bodies. The second method, based on the Froude-Krylov approach, uses numerical integration of dynamic pressures to give forces and moments on any shape hull in any attitude. Unlike the first method, it can be extended to include broaching of the sea surface by the body. Hydrodynamic forces due to an unrestrained body’s motion are accounted for with “added mass” terms.

These mathematical models have been implemented in the C language in a real-time computer simulation. They are actively used to study the dynamic performance and control of submersibles at periscope depths.
Objective and Self-Reported Physical Activity and Risk of Falling Among Community-Dwelling Older Adults From Southern Brazil
Authors: Bielemann Renata M. , Oliveira Ricardo , Bertoldi Andréa Dâmaso , Tomasi Elaine , Demarco Flávio Fernando , Gonzalez Maria Cristina , Bohm Andrea Wendt , Brage Soren , Ekelund Ulf
Published: March 2022

This study evaluated prospective associations between self-reported and objectively measured physical activity (PA) and risk of falls among older adults. A cohort study started in 2014 with 1,451 community-dwelling older adults living in Pelotas, Brazil. Leisure-time PA was obtained by the International Physical Activity Questionnaire and 7-day raw accelerometer data evaluated for total, light PA, and moderate to vigorous PA. In 2016–2017, participants recorded their falls in the previous 12 months. Around 23% of the 1,161 participants followed-up in 2016–2017 experienced a fall in the last 12 months. Participants who did not spend any time in self-reported leisure-time PA at baseline had on average 34% higher risk of falls, and individuals in the lowest tertile for moderate to vigorous PA had on average 51% higher risk of falls compared to those in the highest tertile. Low levels of self-reported and objectively measured moderate to vigorous PA were related to higher risk of falling among Brazilian older adults.
Soil microbiota as game-changers in restoration of degraded lands
Authors: Coban Oksana , De Deyn Gerlinde B. , van der Ploeg Martine
Published: March 2022

Land degradation reduces soil functioning and, consequently, the services that soil provides. Soil hydrological functions are critical to combat soil degradation and promote soil restoration. Soil microorganisms affect soil hydrology, but the role of soil microbiota in forming and sustaining soil is not well explored. Case studies indicate the potential of soil microorganisms as game-changers in restoring soil functions. We review the state of the art of microorganism use in land restoration technology, the groups of microorganisms with the greatest potential for soil restoration, knowledge of the effect of microorganisms on soil physical properties, and proposed strategies for the long-term restoration of degraded lands. We also emphasize the need to advance the emerging research field of biophysical landscape interactions to support soil-plant ecosystem restoration practices.
Addicted to dreaming
Authors: Arrigoni Elda , Fuller Patrick M.
Published: March 2022

How does dopamine, the brain’s pleasure signal, regulate the dream stage of sleep?
Dismantle racism in science
Authors: McGee Ebony Omotola
Published: March 2022

William Shockley Jr. of Stanford University was an American physicist who jointly won the 1956 Nobel Prize in Physics for his role in inventing the transistor. Modern computing and communications would have been unthinkable without Shockley’s work. But the Nobel laureate was also a proponent of eugenics and firmly committed to the racial inferiority of Black people. Shockley was not just a physicist who held racist views. He was part of a wider academic system that then, and now, perpetuates racial inequality. The persistence of this biased ecosystem means that dismantling it will require unrelenting tenacity by all of academia.
New name won’t fix all flaws in China Initiative, critics worry
Authors: Mervis Jeffrey
Published: March 2022

Justice Department promises tighter focus on preventing espionage and no profiling of Chinese academics
Amino Acid-Derived Quorum Sensing Molecule Alanine on the Gastrointestinal Tract Tolerance of the
Lactobacillus
Strains in the Cocultured Fermentation Model
Authors: Wen Jianzhu , Yu Yixing , Chen Mengqi , Cui Lei , Xia Qiang , Zeng Xiaoqun , Guo Yuxing , Pan Daodong , Wu Zhen
Published: March 2022

It was deduced from the study that amino acid-derived metabolites play an important role in cell communication in the gastrointestinal tract (GIT) environment, thus enhancing the communication of
Lactobacillus
strains in the complex fermentation model. Meanwhile, the viability of
Lactobacillus acidophilus
can be increased in the coculture system during the gastrointestinal stress environment treated with the amino acid-derived quorum sensing (QS) molecule
l-
alanine.
Detailed mapping and paleostress analysis of active faults in the northern Vettore–Bove fault zone, Sibillini Mountains, Italy
Authors: Stewart Kevin G. , Boulter Rachel
Published: March 2022

The Sibillini Mountains, which make up the southern part of the Umbria-Marche Apennines, were struck by a series of earthquakes in 2016, including five with magnitudes greater than 5. The largest event, Mw 6.5, occurred on 30 October 2016. A Mw 5.9 earthquake on 26 October ruptured several faults in the northern third of the Vettore–Bove fault system, and the Mw 6.5 event produced surface ruptures along the entire 30-km length. Ground surveys conducted shortly after these earthquakes showed that many, but not all, of the surface ruptures corresponded to previously mapped faults. Also, some faults that had been mapped as Quaternary did not produce surface ruptures during the earthquakes. In this study, we present the results of detailed field mapping that was conducted prior to the 2016 earthquakes and provide evidence that all of the surface ruptures in the northern part of the Vettore–Bove fault system occurred along preexisting faults. Paleostress analysis shows that the reactivated faults had been active prior to 2016 in stress fields with similar orientations to the modern-day stress field. In addition, we show that one fault segment, which is the southern continuation of a major fault that slipped during the 2016 earthquakes, was not reactivated because it was unfavorably oriented.
No evidence of multiple impact scenario across the Cretaceous/Paleogene boundary based on planktic foraminiferal biochronology
Authors: Arz* José A. , Arenillas* I. , Grajales-Nishimura* J.M. , Liesa* C.L. , Soria* A.R. , Rojas* R. , Calmus* T. , Gilabert* V.
Published: March 2022

Large bolide impacts seem to have strongly affected biological evolution, causing detrimental effects on the biosphere. The best-known case is the Chicxulub impact (Yucatan Peninsula, Mexico), the most probable trigger of the Cretaceous/Paleogene boundary (KPB) mass extinction. Nevertheless, after four decades of intensive research, a consensus on the causal relationship between the impact and the mass extinction has not yet been reached. Most of the scientific community has established multiple, strong arguments for the Chicxulub impact as the most likely and principal cause of the KPB mass extinction. However, a variety of hypotheses link the mass extinction mainly to the volcanism of the Deccan Traps and one or more bolide impact events within a relatively short time through the KPB: one impact in the late Maastrichtian (66.3 Ma), corresponding to the Chicxulub impact, a larger one at the KPB (66 Ma), and a final one in the early Danian (65.9 Ma).

Here, we report on the controversies relating to the correlation of the Chicxulub impact event with the mass extinction, with a focus on the stratigraphy and biostratigraphy of sections in Mexico, Cuba, and Haiti, which include ejecta-rich clastic deposits linked to the Chicxulub impact. High-resolution biostratigraphy and quantitative data with planktic foraminifera reveal that these deposits are synchronous with the ejecta-rich airfall layer and the KPB mass extinction horizon of the El Kef, Tunisia, stratotype. Our results provide no support for a multiple impact scenario but confirm that the Chicxulub impact event is indeed the KPB impact event. Furthermore, we have not found any biostratigraphic evidence to support an additional Danian impact event near the Gulf of Mexico region.
Depositional and diagenetic history of travertine deposited within the Anio Novus aqueduct of ancient Rome
Authors: Sivaguru Mayandi , Fouke Kyle W. , Keenan-Jones Duncan , Motta Davide , Garcia Marcelo H. , Fouke Bruce W.
Published: March 2022

Travertine deposits preserved within ancient aqueduct channels record information about the hydrology, temperature, and chemistry of the flowing water from which they precipitated. However, travertine is also chemically reactive and susceptible to freshwater diagenesis, which can alter its original composition and impact reconstructions of aqueduct operation, maintenance, and climate. Hydraulic reconstructions, in combination with a suite of high-resolution optical, laser, electron, and X-ray microscopy analyses, have been used to determine the original crystalline structure and diagenetic alteration of travertine deposited in the Anio Novus aqueduct built in A.D. 38–52 at Roma Vecchia. Age-equivalent travertine deposits, precipitated directly on the mortar-covered floor at upstream and downstream sites along a 140-m-long continuous section of the Anio Novus channel, exhibit consistent crystalline textures and stratigraphic layering. This includes aggrading, prograding, and retrograding sets of travertine linguoid, sinuous, and hummocky crystal growth ripples, as well as sand lags with coated siliciclastic grains deposited on the lee slope of ripple crests. The original aqueduct travertine, which is similar to travertine formed in analogous natural environments, is composed of shrub-like, dendritically branching aggregates of 1–3-μm-diameter euhedral calcite crystals. Dark brown organic matter-rich laminae, formed by microbial biofilms and plant debris, create stratigraphic sequences of high-frequency, dark–light layering. This hydraulic and petrographic evidence suggests that large, radiaxial calcites diagenetically replaced the original aqueduct travertine shrubs, forming upward-branching replacement crystals that crosscut the biofilm laminae. While this diagenetic process destroyed the original crystalline fabric of the calcite shrubs, the entombed biofilm laminae were mimetically preserved. These integrated approaches create the type of depositional and diagenetic framework required for future chemostratigraphic analyses of travertine deposited in the Anio Novus and other ancient water conveyance and storage systems around the world, from which ancient human activity and climatic change can be more accurately reconstructed.