bluuebunny/crossref_metadata_2025 huggingface dataset:
Microbial signatures of health, gingivitis, and periodontitis
Authors: Abusleme Loreto , Hoare Anilei , Hong Bo‐Young , Diaz Patricia I.
Published: March 2021

The subgingival crevice harbors diverse microbial communities. Shifts in the composition of these communities occur with the development of gingivitis and periodontitis, which are considered as successive stages of periodontal health deterioration. It is not clear, however, to what extent health‐ and gingivitis‐associated microbiota are protective, or whether these communities facilitate the successive growth of periodontitis‐associated taxa. To further our understanding of the dynamics of the microbial stimuli that trigger disruptions in periodontal homeostasis, we reviewed the available literature with the aim of defining specific microbial signatures associated with different stages of periodontal dysbiosis. Although several studies have evaluated the subgingival communities present in different periodontal conditions, we found limited evidence for the direct comparison of communities in health, gingivitis, and periodontitis. Therefore, we aimed to better define subgingival microbiome shifts by merging and reanalyzing, using unified bioinformatic processing strategies, publicly available 16S ribosomal RNA gene amplicon datasets of periodontal health, gingivitis, and periodontitis. Despite inherent methodological differences across studies, distinct community structures were found for health, gingivitis, and periodontitis, demonstrating the specific associations between gingival tissue status and the subgingival microbiome. Consistent with the concept that periodontal dysbiosis is the result of a process of microbial succession without replacement, more species were detected in disease than in health. However, gingivitis‐associated communities were more diverse than those from subjects with periodontitis, suggesting that certain species ultimately become dominant as dysbiosis progresses. We identified the bacterial species associated with each periodontal condition and prevalent species that do not change in abundance from one state to another (core species), and we also outlined species co‐occurrence patterns via network analysis. Most periodontitis‐associated species were rarely detected in health but were frequently detected, albeit in low abundance, in gingivitis, which suggests that gingivitis and periodontitis are a continuum. Overall, we provide a framework of subgingival microbiome shifts, which can be used to generate hypotheses with respect to community assembly processes and the emergence of periodontal dysbiosis.
Spatial scale in analysis of the dental plaque microbiome
Authors: Borisy Gary G. , Valm Alex M.
Published: March 2021

Ecologists have long recognized the importance of spatial scale in understanding structure‐function relationships among communities of organisms within their environment. Here, we review historical and contemporary studies of dental plaque community structure in the context of three distinct scales: the micro (1‐10 µm), meso (10‐100 µm) and macroscale (100 µm to ≥1 cm). Within this framework, we analyze the compositional nature of dental plaque at the macroscale, the molecular interactions of microbes at the microscale, and the emergent properties of dental plaque biofilms at the mesoscale. Throughout our analysis of dental plaque across spatial scales, we draw attention to disease and health‐associated structure‐function relationships and include a discussion of host immune involvement in the mesoscale structure of periodontal disease–associated biofilms. We end with a discussion of two filamentous organisms, Fusobacterium nucleatum and Corynebacterium matruchotii, and their relevant contributions in structuring dental plaque biofilms.
Estimating Optimal Treatment Rules with an Instrumental Variable: A Partial Identification Learning Approach
Authors: Pu Hongming , Zhang Bo
Published: March 2021

Individualized treatment rules (ITRs) are considered a promising recipe to deliver better policy interventions. One key ingredient in optimal ITR estimation problems is to estimate the average treatment effect conditional on a subject’s covariate information, which is often challenging in observational studies due to the universal concern of unmeasured confounding. Instrumental variables (IVs) are widely used tools to infer the treatment effect when there is unmeasured confounding between the treatment and outcome. In this work, we propose a general framework of approaching the optimal ITR estimation problem when a valid IV is allowed to only partially identify the treatment effect. We introduce a novel notion of optimality called ‘IV-optimality’. A treatment rule is said to be IV-optimal if it minimizes the maximum risk with respect to the putative IV and the set of IV identification assumptions. We derive a bound on the risk of an IV-optimal rule that illuminates when an IV-optimal rule has favourable generalization performance. We propose a classification-based statistical learning method that estimates such an IV-optimal rule, design computationally efficient algorithms, and prove theoretical guarantees. We contrast our proposed method to the popular outcome weighted learning (OWL) approach via extensive simulations, and apply our method to study which mothers would benefit from travelling to deliver their premature babies at hospitals with high-level neonatal intensive care units. R package ivitr implements the proposed method.
Professional values and nursing self‐efficacy in the Italian context. Correlational descriptive study
Authors: Dellafiore Federica , Rosa Debora , Udugampolage Nathasha Samali , Villa Giulia , Albanesi Beatrice
Published: March 2021

Introduction

Nurses’ professional values (NPVs) and self‐efficacy (SE) are two fundamental elements in nursing care that influence its professional identity, competences, resulting in changing the behaviour of professionals and their response to the patient's health needs. The various studies produced so far have not investigated a possible relationship between these two areas. Therefore, the objective of the following study is to identify and deepen the relationship between NPV and SE, in order to improve the knowledge of these issues.

Materials and methods

An observational, correlational and multicentric study has been carried out through a questionnaire based survey. The sampling was conventional. The data collection took place through Nursing Professional Values Scale, version 3 (NPVS‐3), which investigates professional values; and Nursing Professional Self‐Efficacy Scale (NPSES), which investigates self‐efficacy and a socio‐demographic questionnaire.

Results

The total sample was 532 nurses and 65.6% was female, with a median age of 42 years and a median of 15 working years. Positive statistically significant correlations between the various domains of the NPVS‐3 and NPSES scales were found. These relationships also emerged in the analyses between geographical areas. Overall, the relationships between self‐efficacy and values were similar in all the analyses.

Discussion

As the professional values of nurses increase in their response to the patient's health needs, self‐efficacy perceived by them increases and vice versa, significantly effecting the clinic and care outcomes of the patients and improving nursing outcomes. The stratification of the sample by geographical area regarding the relationship between age, years of work and professional values indicated that these variables strongly influence the NPV and SE of nurses. Therefore, in some contexts, more support in maintaining a stable value structure may be needed; moreover, it is necessary to incentivise nurses with more effective interventions, as an example and a basis of motivation for future generations.
Suitability of high‐frequency ultrasonography (20 MHz) in evaluation of various forms of primary cicatricial alopecia in relation to trichoscopy — pilot study
Authors: Mikiel Dominik , Polańska Adriana , Żaba Ryszard , Adamski Zygmunt , Dańczak‐Pazdrowska Aleksandra
Published: March 2021

Background

Primary cicatricial alopecia is a potentially irreversible process of hair loss, in which for proper diagnosis a skin biopsy is necessary. Searching for new, non‐invasive diagnostic methods may shorten the time for final diagnosis, initiating appropriate treatment and reduce the need for biopsy. The aim of this study was to evaluate the usefulness of high‐frequency ultrasonography (HF‐USG) as a diagnostic method in patients with primary scarring alopecia and to compare it with trichoscopy.

Materials and methods

The study covered a total of 44 adults: 8 with classic lichen planopilaris (LPP), 11 with discoid lupus erythematosus (DLE), 14 with frontal fibrosing alopecia (FFA), and 11 healthy volunteers. Each patient underwent physical and trichoscopic examination which was the base for qualification for active/inactive stage of the disease. Then, HF‐USG was performed using a probe with a frequency of 20 MHz. In HF‐USG images, the following elements were evaluated and measured: entrance echo (EE), follicular structures (FS), dermal background (DB), and dermal/subdermal border (D/SB).

Results

Inactive phase was characterized by significantly lower number/lack of FS compared to the active phase of scarring alopecia. HF‐USG of active LPP/FFA presented cigar‐like shaped FS, while inactive stage pronounced D/SB forming saw‐like pattern. Active DLE in HF‐USG were associated with focal, doubled EE and widened FS with a tendency to create hypoechogenic wide, structureless bands within the skin. In inactive DLE, there was no specific pattern of D/SB or rarely puzzle‐like pattern.

Conclusion

HF‐USG images differ depending on the phase of the disease and the type of scarring alopecia, similarly to trichoscopic examination.
In vivo reflectance confocal microscopy of halo nevi
Authors: Pogorzelska‐Antkowiak Anna , Corneli Paola , Agozzino Marina
Published: March 2021

Introduction

Halo nevi named also Sutton's nevi are uncommon melanocytic lesions occurring especially among adolescents. There are two effective diagnostic methods: dermoscopy and in vivo reflectance confocal microscopy (RCM), which can help us to observe many structural elements and characteristic features of Sutton's nevi.

Objectives

The aim of this study was to describe reflectance confocal microscopy features of halo nevi.

Methods

Eleven patients with fourteen halo nevi were examined by FotoFinder Medicam 800 dermoscope and reflectance confocal microscope Viva Scope 1500 between May of 2018 and September of 2019.

Results

Dermoscopic examination revealed 78.6% nevi with a globular pattern, while 21.4% showed a homogenous pattern. In RCM, a typical honeycombed pattern was observed in 57.1% of nevi. 42.9% of nevi showed a disarray of the epidermis and presence of dendritic cells. 35.7% of all lesions presented roundish atypical cells in the epidermis. Roundish pagetoid cells in the dermo‐epidermal junction were detected in 14.2% of nevi. Non‐edged papillae were observed in 50% of lesions. In each nevus, there were dilated vessels. 50% of nevi revealed dense nests in the periphery, although in case of one lesion the dishomogeneous nests were observed.

Conclusions

Halo nevi are important “melanoma simulators” in confocal microscopy.
The role of cryoprecipitate in human and canine transfusion medicine
Authors: Prittie Jennifer
Published: March 2021

Objective

To evaluate the current role of cryoprecipitate in human and canine transfusion medicine.

Data sources

Human and veterinary scientific reviews and original studies found using PubMed and CAB Abstract search engines were reviewed.

Human data synthesis

In the human critical care setting, cryoprecipitate is predominantly used for fibrinogen replenishment in bleeding patients with acute traumatic coagulopathy. Other coagulopathic patient cohorts for whom cryoprecipitate is recommended include those undergoing cardiovascular or obstetric procedures or patients bleeding from advanced liver disease. Preferential selection of cryoprecipitate versus fibrinogen concentrate (when available) is currently being investigated. Also a matter of ongoing debate is whether to administer this product as part of a fixed‐dose massive hemorrhage protocol or to incorporate it into a goal‐directed transfusion algorithm applied to the individual bleeding patient.

Veterinary data synthesis

Although there are sporadic reports of the use of cryoprecipitate in dogs with heritable coagulopathies, there are few to no data pertaining to its use in acquired hypofibrinogenemic states. Low fibrinogen in dogs (as in people) has been documented with acute traumatic coagulopathy, advanced liver disease, and disseminated intravascular coagulation. Bleeding secondary to these hypocoagulable states may be amenable to cryoprecipitate therapy. Indications for preferential selection of cryoprecipitate (versus fresh frozen plasma) remain to be determined.

Conclusions

In the United States, cryoprecipitate remains the standard of care for fibrinogen replenishment in the bleeding human trauma patient. Its preferential selection for this purpose is the subject of several ongoing human clinical trials. Timely incorporation of cryoprecipitate into the transfusion protocol of the individual bleeding patient with hypofibrinogenemia may conserve blood products, mitigate adverse transfusion‐related events, and improve patient outcomes. Cryoprecipitate is readily available, effective, and safe for use in dogs. The role of this blood product in clinical canine patients with acquired coagulopathy remains unknown.
Ultrasonographic guidance for perineural injections of the cervical spinal nerves in horses
Authors: Wood Andrew Douglas , Sinovich Matthew , Prutton James Stephen Winter , Parker Russell Alexander
Published: March 2021

Objective

To evaluate the accuracy of ultrasonographic guidance for injection near the ventral rami of the cervical spinal nerves (VRCSN).

Study design

Ex vivo study.

Sample population

Ten cadavers (n = 40 injections).

Methods

Left and right VRCSN at C4/5 and C5/6 were infiltrated at the intervertebral foramen (IVF) under ultrasonographic guidance. A vertically orientated 3.5‐MHz curvilinear probe was used to identify the craniocaudal midpoint of the articular process joint (APJ). The probe was moved ventrally until the IVF was identified. An 18‐gauge 15‐cm‐long spinal needle was aimed immediately below the ventral margin of the cranial articular process, where 1 mL of latex was injected. Cadavers were dissected, and the location of the latex was recorded relative to the ventral ramus, the spinal cord, and the vertebral artery.

Results

Direct infiltration of the ventral ramus occurred in 73% (29/40) of injections; 15% (6/40) of injections were < 0.5 cm from the ventral ramus, and 13% (5/40) of injections were > 0.5 cm (maximum 1.5 cm). Latex was located at a mean of 2.4 cm (range, 0.8–4) from the spinal cord and 0.9 cm (range, 0–1.5) from the vertebral artery.

Conclusion

Ultrasonographic guidance of perineural injections of the caudal VRCSN was repeatable and accurate, with 88% of injections located within 0.5 cm of the ventral ramus. Iatrogenic damage was limited to one penetration into the vertebral artery.

Clinical significance

Ultrasonographic guidance of perineural injections of the caudal VRCSN may be considered by operators experienced in cervical APJ scanning in horses with suspected cervical spinal nerve compression.
An Empirical Research Survey of the Productivity and Efficiency of the Securities Industry
Authors: Tran My , Abbott Malcolm
Published: March 2021

This paper provides a review of the approaches that have been used to evaluate the productivity and efficiency of the securities industry (financial ratios, econometric techniques, data envelopment analysis-DEA, and the estimation of stochastic frontiers). In undertaking this it identifies some of the organisational structure characteristics of securities companies that are associated with high levels of operational efficiency, particularly regarding the impact of regulation, the structure of ownership, and economies of scope and scale. The findings are that from the limited number of studies that have to date been undertaken it appears that the industry does have economies of scale, benefits from deregulation and performs better with foreign and bank ownership.
Heterotopic Place-Making in Learning Environments: Children Living as Creative Citizens
Authors: Adlerstein-Grimberg Cynthia Yael , Bralic-Echeverría Andrea
Published: March 2021

This paper reconceptualizes children as already-being- citizens within kindergarten learning environments. It draws on Foucauldian heterotopology to show what type of heterotopias entangle two and three-year-old in everyday place-making practices and how they empower themselves to inhabit learning environments as creative citizens. After a collaborative ethnographic immersion in 16 Chilean public kindergartens during the academic year 2019, findings show three types of heterotopic place-making that enact children’s citizenship: Unpredictable movements and wanderings, new ruling artifacts, and serendipitous spatial transgressions. We discuss how these unsettle ECE learning environment utopias and invite teachers’ improvisatory practices for alternative spatialities and children’s creative citizenship.
A Velocity-Modified Temperature for the Plastic Flow of Metals
Authors: MacGregor C. W. , Fisher J. C.
Published: March 2021

Based on the work of Eyring and others relating to the creep problem, a velocity-modified temperature is developed for representing by means of a single variable the combined effects of strain rate and temperature on the stress reaction in a tension specimen. Available data are analyzed, indicating that the velocity-modified temperature is equally applicable to the tension test conducted at both slow and rapid rates and to the creep test. The data also indicate that the stress reaction, corresponding to tests at very slow and very rapid rates of deformation, may be found from tension tests at moderate strain rates and appropriately raised or lowered temperatures.
A Uniform Method for Determining Angular Accelerations in Mechanisms
Authors: Koenig L. R.
Published: March 2021

The purpose of this paper is to disclose a more reliable and uniform method, applicable to mechanisms in general, for determining directly the angular accelerations of the constituent links. The method completely suffices where the determination of angular accelerations is the end in view. Although it is independent of normal, tangential, and total accelerations of points on the links, reliable determinations of such accelerations are considerably facilitated with the aid of the acquired angular accelerations. Angular-acceleration problems may be solved with increased assurance because; (a) only velocity-vector considerations are required in the necessary kinematic layouts; (b) full advantage may be taken of the process of inversion in simplifying velocity-vector layouts, which is not possible when acceleration vectors are employed; and (c) the method gives considerable insight into the effects of the various factors controlling the angular accelerations.
Action of Forces and Moments Symmetrically Distributed Along a Generatrix of a Thin Cylindrical Shell
Authors: Odqvist F. K. G.
Published: March 2021

Applications of the present subject theory have been made to monolithic structures by certain Scandinavian engineers who have treated the subject and related problems in a series of papers. The author has confined his studies to more slender structures, such as welded and riveted plate containers, ship hulls, and similar applications, to which a simplified form of the theory may be applied. For an isotropic shell with no stiffeners, explicit formulas are developed in important cases, where the external load is applied to a cylindrical shell, distributed along a generatrix.
Equivalent Circuits for the Numerical Solution of the Critical Speeds of Flexible Shafts
Authors: Kron Gabriel
Published: March 2021

A special type of equivalent circuit is developed that is particularly suited for the numerical calculation of the critical speeds of uniformly rotating shafts. The shaft may consist of several spans rotating in flexible bearings supported by a flexible foundation. Either the various spans may be asymmetrical along two principal axes or the bearings may have asymmetrical flexibilities. The same circuits are, of course, valid also for the study of the natural frequency of vibration of a skewed asymmetrical beam held by flexible supports at several points, such as a turbine bucket. The circuits may be solved by slide rule, by punch-card methods, or by a “network analyzer.” The procedure is self-checking as the correctness of the numbers may be checked at any stage of the calculations. For the symmetrical case, the results are identical with those found by the method of Prohl (1) or Myklestad (2), even though the circuit method requires fewer calculations. In general, the equivalent circuits for the various spans, bearings, overhung loads, and foundations are independent and are interchangeable for different combinations of shaft structure. Also, any variation in a component part leaves the circuits of the other parts unchanged. A punch-card study of a turbine generator shaft with fixed bearings carrying a high-pressure turbine, a low-pressure turbine, and a generator is given in a companion paper by A. W. Rankin (3).
Local Stress Distribution in Cylindrical Shells
Authors: Beskin Leon
Published: March 2021

The stress distribution in cylindrical shells with light frames is very different from the conventional beam distribution in the neighborhood of the applied loads. The problem is examined hereafter for circular cylinders with circular frames of constant section. The case of an indefinite shell with one loaded frame is examined in detail, and diagrams are given for the following unit conditions: Concentrated radial force, tangential force, couple.
A Photoelectric Method of Measuring Damping in Metal Forks at Elevated Temperatures
Authors: Pochapsky T. E. , Mase W. J.
Published: March 2021

Engineering measurements of internal friction in metals have been obtained from the decay characteristics of tuning forks of metals of interest. A damping program at Battelle Memorial Institute, conducted for the Office of Scientific Research and Development, called for such measurements at temperatures up to 1500 F, and it was necessary to develop suitable apparatus for obtaining accurate results at those elevated temperatures. A photoelectric method of measuring tine amplitude decay, using shutters on a vibrating fork to modulate light directed at a photocell, was developed. It proved to give very satisfactory results and had none of the mechanical difficulties in operation and uncertainties in results that were encountered at high temperatures when platinum-wire Sauereisen-cemented strain gages were used. It was necessary to reduce energy losses from the fork to its support by using a compliant coupling. This suspension worked so well that the lower limit of decrement measurements was probably determined by acoustic losses. It is believed that such losses added less than 0.00004 to the decrements of steel forks. This report includes details of construction of the equipment and reviews tests performed to establish its accuracy.
Concentrated-Force Problems in Plane Strain, Plane Stress, and Transverse Bending of Plates
Authors: Symonds P. S.
Published: March 2021

A general method is described for the solution of problems of transverse bending of thin plates acted on by concentrated normal forces, and of problems of plane stress or plane strain, in which concentrated forces are applied to the boundaries. The solution is taken in two parts: (a) The special functions which give the stresses or deflections in the neighborhood of the concentrated forces. (b) A complementary function, satisfying the appropriate biharmonic equation, such that the complete solution satisfies the boundary conditions of the problem. For certain types of boundaries, this complementary function can be determined by expanding the concentrated-force functions as infinite trigonometric series. Then by addition of general solutions of the appropriate biharmonic equation, the required boundary conditions may be satisfied. The method is first illustrated by solving the plate-bending problem, for which the solution is known, of a clamped circular disk loaded by a transverse force at any point. It is then applied to the problem of an infinite plate fixed at an inner circular boundary, with outer edge free, and loaded by a transverse force at any point. This solution is obtained in finite form, and typical curves of deflection, bending moments, and shear forces are given in Figs. 3 to 8, inclusive. Using this result, solutions are next obtained for ring-shaped plates of finite outer radius, with the force applied either at the outer edge or at any point between the inner clamped edge and the outer free edge. The former case was previously solved by H. Reissner. Curves comparing the maximum moments and shears in the infinite plate with those of the annular plate with force either at the outer edge, or inside the ring are given in Figs. 9 to 12, inclusive. Finally, a solution is given of the problem in plane stress of a large plate containing an elliptical hole, which is loaded by line forces at the ends of the minor axes of the ellipse. Curves showing results of this solution are given in Figs. 14 and 15.
The Influence of Oil-Film Journal Bearings on the Stability of Rotating Machines
Authors: Hagg A. C.
Published: March 2021

The self-excited vibration caused by the lubricating films of journal bearings and commonly called oil-film whirl or oil whip is discussed. The upper limit of whirling frequency has been found to be one-half rotational frequency in the general case; actually the phenomenon will manifest itself at a frequency which is invariably below this limit. Stability criteria have been developed for certain common systems in terms of bearing and rotor parameters. The tilting-pad bearing of Michell has been established as a so-called “stable” or “nonwhirling” bearing. This bearing and related types are probably the only oil-film journal bearings which are incapable of exciting oil whip, regardless of the system to which they are applied. Qualitatively the results of the paper appear to be in agreement with observations. In certain cases, results have been substantiated experimentally.
Analytical Design of Centrifugal Air Compressors
Authors: Concordia C. , Dowell M. F.
Published: March 2021

The object of this paper is to describe a general method of design and analysis which has been developed for, and applied primarily to, the design of supercharger centrifugal impellers. The method has also been used as a systematic means for the analysis of such impellers as well as for the design of the corresponding diffusers and of gas-turbine compressors and turbines. The development was undertaken with the idea of obtaining, as nearly as possible, a self-sufficient and self-contained rational design method which would be influenced as little as possible by preconceived notions of what the impeller blades should look like. The method is also complete in the sense that it is not used merely as a guide to the character of the blade shape, e.g., to determine limiting curvatures. Instead, one starts from and uses the basic laws of the fluid motion to determine the required flow path and thus the complete blade shape. On the other hand, the fullest use has been made of available experience and test results as checks of the theory.
An Improved Fuse Escapement for the Mark 18 and Other U. S. Navy Mechanical Time Fuses
Authors: Kelly F. G. , Zar J. L.
Published: March 2021

Theoretical shortcomings of previous Army and Navy fuse escapements are pointed out. The development of a new escape wheel and lever is described, in which spurious torques due to the fall of escape-wheel teeth against the pallets are eliminated; and a tooth shape is derived which delivers accelerating impulses symmetrically about the neutral position of the lever. Fuses with the new escapement have a timing rate which is independent of driving torque over the range of torques encountered; they can be assembled with one size of wheel and lever and with no hand-matching, function at low driving torques, and have given improved firing-test performance.
The Theory of Curved Beams
Authors: Best G. C.
Published: March 2021

In this paper, the theory of curved beams is developed by a somewhat different procedure from that customarily employed. Deflections at the centroid are first assumed and then loads and stresses resulting from these deflections are estimated. This process works out in a somewhat more orderly fashion than the conventional development. Throughout, all measurements are to the centroidal axis rather than to the neutral axis. Final results are presented in such a form that satisfactory accuracy may be obtained from slide-rule computations and approximate integration. Hence the procedure is applicable to any section, it being unnecessary first to develop a special formula for each different section. An illustrative example is given. The theory is extended to cover the case of unsymmetrical bending of curved beams. The effects of torsion, which will probably also occur in the generalized case, are not treated. These can be superimposed upon stresses due to bending.
Reconstructing Compressor Nonuniform Circumferential Flow Field From Spatially Undersampled Data—Part 2: Practical Application for Experiments
Authors: Lou Fangyuan , Matthews Douglas R. , Kormanik Nicholas J. , Key Nicole L.
Published: March 2021

In the previous part of the paper, a novel method to reconstruct the compressor nonuniform circumferential flow field using spatially undersampled data points is developed. In this part of the paper, the method is applied to two compressor research articles to further demonstrate the potential of the novel method in resolving the important flow features associated with these circumferential nonuniformities. In the first experiment, the static pressure field at the leading edge of a vaned diffuser in a high-speed centrifugal compressor is reconstructed using pressure readings from nine static pressure taps placed on the hub of the diffuser. The magnitude and phase information for the first three dominant wavelets are characterized. Additionally, the method shows significant advantages over the traditional averaging methods for calculating repeatable mean values of the static pressure. While using the multi-wavelet approximation method, the errors in the mean static pressure with one dropout measurement are 70% less than the pitchwise-averaging method. In the second experiment, the full annulus total pressure field downstream of Stator 2 in a three-stage axial compressor is reconstructed from a small segment of data representing 20% coverage of the annulus. Results show very good agreement between the reconstructed total pressure profile and the experiment at a variety of spanwise locations from near hub to near shroud. The features associated with blade row interactions accounting for passage-to-passage variations are resolved in the reconstructed total pressure profile.
Steady and Unsteady Temperature Measurements in the Wake of a Linear Cascade With Heated Airfoils
Authors: Aberle-Kern Svenja , Ripplinger Thomas , Niehuis Reinhard
Published: March 2021

Understanding basic aerodynamic and thermodynamic processes in engine components is critical to achieving higher efficiencies and lower fuel consumption in aircraft engines. To aid in this process, a linear compressor cascade was investigated in the high-speed cascade wind tunnel of the Institute of Jet Propulsion to quantify the influence of heat transfer on the temperature distribution in the wake and, finally, the profile loss. For this purpose, a patented five-hole probe with an integrated thermocouple was developed and applied for steady measurements. Additionally, a hot-wire measurement setup was implemented to receive temperature fluctuations via the constant current (CC) mode as well as velocity fluctuations via the constant temperature (CT) mode. A novel method for a two-way temperature and velocity correction for the two types of hot-wire measurement is presented. Good agreement between the measurement data of the five-hole probe and averaged data from hot-wire anemometry was found. The temperature distribution indicates the occurrence of energy separation which in some cases is overlain with the effects of heat transfer. In addition, the analysis of unsteady fluctuations of temperature and velocity give more detailed information about the vortex shedding in the wake, including the size of the vortices. Finally, this is the first discussion of energy separation at a compressor cascade combined with overlain effects of heat transfer on the blade surface.
A Machine-Learnt Wall Function for Rotating Diffusers
Authors: Tieghi Lorenzo , Corsini Alessandro , Delibra Giovanni , Tucci Francesco Aldo
Published: March 2021

Data-driven tools and techniques have proved their effectiveness in many engineering applications. Machine-learning has gradually become a paradigm to explore innovative designs in turbomachinery. However, industrial computational fluid dynamics (CFD) experts are still reluctant to embed similar approaches in standard practice and very few solutions have been proposed so far. The aim of the work is to prove that standard wall treatments can obtain serious benefits from machine-learning modeling. Turbomachinery flow modeling lives in a constant compromise between accuracy and the computational costs of numerical simulations. One of the key factors of the process is defining a proper wall treatment. Many works point out how insufficient resolutions of boundary layers may lead to incorrect predictions of turbomachinery performances. Wall functions are universally exploited to replicate the physics of boundary layers where grid resolution does not suffice. Widespread wall functions were derived by the observation of a few canonical flows, further expressed as a simple polynomial of Reynolds number and turbulent kinetic energy. Despite their popularity, these functions are frequently applied in flows where the ground assumptions cease to be true, such as rotating passages or swirled flows. In these flows, the mathematical formulations of wall functions do not account for the distortion on the boundary layer due to the combined action of centrifugal and Coriolis forces. Here, we will derive a wall function for rotating passages, through means of machine-learning. The algorithm is directly implemented in the NS equations solver. Cross-validation results show that the machine-learnt wall treatment is able to effectively correct the turbulent kinetic energy field near the solid walls, without impairing the accuracy of the Reynolds-averaged numerical simulations (RANS) turbulence model in any way.
Experimental Investigation of Tip Design Effects on the Unsteady Aerodynamics and Heat Transfer of a High-Speed Turbine
Authors: Cernat Bogdan C. , Lavagnoli Sergio
Published: March 2021

While modern engine manufacturers devote significant efforts to the development of reliable and efficient machines, the introduction of novel, optimized components in the hot gas path represents a risky opportunity. Accurate experimental and numerical data are critical to assess the impact of new technologies on the harsh engine environment. The present study addresses the impact of a selection of high-performance rotor blade tips on the aerodynamic and heat flux field of a high-pressure turbine (HPT) stage. A combined numerical and experimental approach is employed to characterize the interaction of the tip leakage flow with the rotor secondary flows and the casing heat transfer mechanisms for each individual tip geometry. The turbine stage is tested at engine-scaled conditions in the rotating turbine facility of the von Karman Institute. In the present study, the turbine rotor is operated in rainbow configuration to allow the simultaneous testing of multiple blade tip geometries. Reynolds-averaged Navier–Stokes (RANS) simulations are employed to predict the aerodynamic and thermal fields of the individual profiles using test-calibrated boundary conditions. Isothermal steady computations are performed at different wall temperatures to compute the adiabatic wall temperature and the heat transfer convective coefficient. Low-order models are used to represent the over-tip thermal field and the driving heat transfer mechanisms. The time-resolved outlet flow is characterized using a vortex tracking technique and high-frequency aerodynamic measurements to identify the rotor secondary flow structures.
Single and Multiple Circumferential Casing Groove for Stall Margin Improvement in a Transonic Axial Compressor
Authors: Mustaffa A. F. , Kanjirakkad V.
Published: March 2021

The stability limit of a tip-stalling axial compressor is sensitive to the magnitude of the near-casing blockage. In transonic compressors, the presence of the passage shock could be a major cause for the blockage. Identification and elimination of this blockage could be a key to improving the stability limit of the compressor. In this article, using numerical simulation, the near-casing blockage within the transonic rotor, NASA Rotor 37, is quantified using a blockage parameter. For a smooth casing, the blockage at conditions near stall is maximum at about 20% of the tip axial chord downstream of the tip leading edge. This maximum blockage location is found to be consistent with the location of the passage shock–tip leakage vortex interaction. A datum single casing groove design that minimizes the peak blockage is found through an optimization approach. The stall margin improvement of the datum casing groove is about 0.6% with a negligible efficiency penalty. Furthermore, the location of the casing groove is varied upstream and downstream of the datum location. It is shown that the stability limit of the compressor is best improved when the blockage is reduced upstream of the peak blockage location. This article also discusses the prospects of a multigroove casing configuration.
Detailed Experimental Study of the Flow in a Turbine Rear Structure at Engine-Realistic Flow Conditions
Authors: Vikhorev Valentin , Chernoray Valery , Thulin Oskar , Deshpande Srikanth , Larsson Jonas
Published: March 2021

A good aerodynamic design of the turbine rear structure (TRS) is crucial for improving efficiency and reducing emissions from aero-engines. This paper presents a detailed experimental evaluation of an engine-realistic TRS which was studied in an engine-realistic rig at Chalmers University of Technology, Sweden. The TRS test section was equipped with three types of outlet guide vanes (OGVs) which are typical of modern state-of-the-art TRS: regular vanes, thickened vanes, and vanes with an engine-mount recess (a shroud bump). Each of the three vane geometries was studied under on-design and off-design conditions at a fixed flow Reynolds number of 235,000. The study shows that the off-design performance of the TRS strongly depends on the presence of the local flow separation on the OGV suction side near the hub, which is greatly affected by the vane pressure distribution and inlet conditions. Similarly, the OGVs with increased thickness and with a vane shroud bump are shown to affect the performance of the TRS by influencing the losses on the OGV suction side near the hub. Furthermore, the presence of the bump is shown to have a noticeable upstream influence on the outlet flow from the low-pressure turbine and a noticeable downstream influence on the outlet flow from the TRS.
Uncertainty Evaluation on Multi-Hole Aerodynamic Pressure Probes
Authors: Notaristefano Andrea , Gaetani Paolo , Dossena Vincenzo , Fusetti Alberto
Published: March 2021

In the frame of a continuous improvement of the performance and accuracy in the experimental testing of turbomachines, the uncertainty analysis on measurements instrumentation and techniques is of paramount importance. For this reason, since the beginning of the experimental activities at the Laboratory of Fluid Machines (LFM) located at Politecnico di Milano (Italy), this issue has been addressed and different methodologies have been applied. This paper proposes a comparison of the results collected applying two methods for the measurement uncertainty quantification to two different aerodynamic pressure probes: sensor calibration, aerodynamic calibration and probe application are considered. The first uncertainty evaluation method is the so-called “uncertainty propagation” method (UPM); the second is based on the “Monte Carlo” method (MCM). Two miniaturized pressure probes have been selected for this investigation: a pneumatic five-hole probe and a spherical fast-response aerodynamic pressure probe (sFRAPP), the latter applied as a virtual four-hole probe. Since the sFRAPP is equipped with two miniaturized pressure transducers installed inside the probe head, a specific calibration procedure and a dedicated uncertainty analysis are required.
High-Fidelity Simulations of a High-Pressure Turbine Vane Subject to Large Disturbances: Effect of Exit Mach Number on Losses
Authors: Zhao Yaomin , Sandberg Richard D.
Published: March 2021

We report on a series of highly resolved large-eddy simulations of the LS89 high-pressure turbine (HPT) vane, varying the exit Mach number between Ma = 0.7 and 1.1. In order to accurately resolve the blade boundary layers and enforce pitchwise periodicity, we for the first time use an overset mesh method, which consists of an O-type grid around the blade overlapping with a background H-type grid. The simulations were conducted either with a synthetic inlet turbulence condition or including upstream bars. A quantitative comparison shows that the computationally more efficient synthetic method is able to reproduce the turbulence characteristics of the upstream bars. We further perform a detailed analysis of the flow fields, showing that the varying exit Mach number significantly changes the turbine efficiency by affecting the suction-side transition, blade boundary layer profiles, and wake mixing. In particular, the Ma = 1.1 case includes a strong shock that interacts with the trailing edge, causing an increased complexity of the flow field. We use our recently developed entropy loss analysis (Zhao and Sandberg, 2019, “Using a New Entropy Loss Analysis to Assess the Accuracy of RANS Predictions of an HPT Vane,” ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition, Paper No. GT2019-90126) to decompose the overall loss into different source terms and identify the regions that dominate the loss generation. Comparing the different Ma cases, we conclude that the main mechanism for the extra loss generation in the Ma = 1.1 case is the shock-related strong pressure gradient interacting with the turbulent boundary layer and the wake, resulting in significant turbulence production and extensive viscous dissipation.
Sequential Self-Folding of Shape Memory Polymer Sheets by Laser Rastering Toward Origami-Based Manufacturing
Authors: Abdulhafez Moataz , Line Joshua , Bedewy Mostafa
Published: March 2021

Origami-based fabrication strategies open the door for developing new manufacturing processes capable of producing complex three-dimensional (3D) geometries from two-dimensional (2D) sheets. Nevertheless, for these methods to translate into scalable manufacturing processes, rapid techniques for creating controlled folds are needed. In this work, we propose a new approach for controlled self-folding of shape memory polymer sheets based on direct laser rastering. We demonstrate that rapidly moving a CO2 laser over pre-strained polystyrene sheets results in creating controlled folds along the laser path. Laser interaction with the polymer induces localized heating above the glass transition temperature with a temperature gradient across the thickness of the thin sheets. This gradient of temperature results in a gradient of shrinkage owing to the viscoelastic relaxation of the polymer, favoring folding toward the hotter side (toward the laser source). We study the influence of laser power, rastering speed, fluence, and the number of passes on the fold angle. Moreover, we investigate process parameters that produce the highest quality folds with minimal undesired deformations. Our results show that we can create clean folds up to and exceeding 90 deg, which highlights the potential of our approach for creating lightweight 3D geometries with smooth surface finishes that are challenging to create using 3D printing methods. Hence, laser-induced self-folding of polymers is an inherently mass-customizable approach to manufacturing, especially when combined with cutting for integration of origami and kirigami.
A Computational Efficient Approach to Compute Temperature for Energy Beam Additive Manufacturing
Authors: Ou Chun-Yu , Richard Liu C.
Published: March 2021

Temperature history prediction is essential for a better understanding of the relationship between microstructural change and processing conditions for energy beam additive manufacturing fabricated components. Here, a new efficient approach combining a moving heat source analytical model with a melting and solidification model is presented. An innovative method is proposed to compute the “effective computation zone” as a boundary condition, which can save computation time significantly. Notably, the computational efficiency can improve by 104–105 compared with finite element models. With this range of improvement efficiency, the temperature predicted based on this method is consistent (around 9% of average deviation) with experimental measurements by the thermocouple. This model can be used as a reference to define the boundary condition for further complex numerical analysis with improved accuracy at a reduction of efficiency as desired. In addition, it can be used as a reference to determine processing conditions that would allow the efficient and effective control of the temperature history within a range for a certain microstructure design.
Deep transfer learning for underwater direction of arrival using one vector sensor
Authors: Cao Huaigang , Wang Wenbo , Su Lin , Ni Haiyan , Gerstoft Peter , Ren Qunyan , Ma Li
Published: March 2021

A deep transfer learning (DTL) method is proposed for the direction of arrival (DOA) estimation using a single-vector sensor. The method involves training of a convolutional neural network (CNN) with synthetic data in source domain and then adapting the source domain to target domain with available at-sea data. The CNN is fed with the cross-spectrum of acoustical pressure and particle velocity during the training process to learn DOAs of a moving surface ship. For domain adaptation, first convolutional layers of the pre-trained CNN are copied to a target CNN, and the remaining layers of the target CNN are randomly initialized and trained on at-sea data. Numerical tests and real data results suggest that the DTL yields more reliable DOA estimates than a conventional CNN, especially with interfering sources.