Although Western blots are frequently quantified, densitometry is not documented and appears to be based merely on traditions and guesswork. Confirming previous experience, none of 100 randomly ...selected and systematically scanned most recent papers provided sufficient information on how Western blot results were translated into statistical values. The importance of such information, however, becomes evident from our correlations of plasma erythropoietin values of various mammals determined using RIA and Western blot densitometry. Different common densitometry procedures applied to the identical Western blot revealed p-values of these correlations ranging from 0.000013 to 0.76 reflecting the necessity of a scientifically sound basis for densitometry of Western blots. At present, the current lack of any definitions in densitometry opens the door to uncontrollable acquisition of any desired p-value. Here we provide data that define what should be considered, what avoided and what documented when quantifying Western blots.
X‐ray microdensitometry on annually resolved tree‐ring samples has gained an exceptional position in last‐millennium paleoclimatology through the maximum latewood density (MXD) parameter, but also ...increasingly through other density parameters. For 50 years, X‐ray based measurement techniques have been the de facto standard. However, studies report offsets in the mean levels for MXD measurements derived from different laboratories, indicating challenges of accuracy and precision. Moreover, reflected visible light‐based techniques are becoming increasingly popular, and wood anatomical techniques are emerging as a potentially powerful pathway to extract density information at the highest resolution. Here we review the current understanding and merits of wood density for tree‐ring research, associated microdensitometric techniques, and analytical measurement challenges. The review is further complemented with a careful comparison of new measurements derived at 17 laboratories, using several different techniques. The new experiment allowed us to corroborate and refresh “long‐standing wisdom” but also provide new insights. Key outcomes include (i) a demonstration of the need for mass/volume‐based recalibration to accurately estimate average ring density; (ii) a substantiation of systematic differences in MXD measurements that cautions for great care when combining density data sets for climate reconstructions; and (iii) insights into the relevance of analytical measurement resolution in signals derived from tree‐ring density data. Finally, we provide recommendations expected to facilitate futureinter‐comparability and interpretations for global change research.
Plain Language Summary
Paleoclimatology, the study of how the climate has changed throughout earth history, is an important component of climate change research. The wood density of tree rings is a widely used parameter to study past temperature changes. Despite wood density being widely used and considered excellent for this type of research, deriving comparable measurements at different laboratories and using a variety of techniques are proving challenging. This review compiles the current understanding and merits of wood density as a proxy in paleoclimate research. We further describe and review prevalent measurement techniques and associated analytical measurement challenges. The review is also complemented with a careful comparison of a set of new measurements derived at 17 laboratories, using several different techniques. We find that there are substantial differences in measurements performed among laboratories. The main challenge is associated with the analytical resolution when measuring small features such as the density of the latewood. We provide recommendations for future work to overcome systematic differences and towards the prospect of combining measurements from different techniques in integrative studies.
Key Points
We review the merits and state of the art of tree‐ring wood microdensitometry and its associated analytical challenges
We show that systematic level offsets in mean wood density from different techniques and laboratories require correction
Measurement resolution—notoriously difficult to control—is identified as the major challenge for future research applications
Cavitating flow behind a backward facing step Bhatt, Anubhav; Ganesh, Harish; Ceccio, S.L.
International journal of multiphase flow,
June 2021, 2021-06-00, 20210601, Letnik:
139
Journal Article
Recenzirano
Odprti dostop
Flow topology and unsteady cavitation dynamics in the wake of a backward facing step was investigated using high speed videography and time-resolved X-ray densitometry, along with static and dynamic ...pressure measurements. The measurements are used to inform the understanding of underlying mechanisms of observed flow dynamics as they are related to shock wave induced instabilities. The differences in cavity topology and behavior at different cavitation numbers are examined to highlight flow features such as the pair of cavitating spanwise vortices in the shear layer and propagating bubbly shock front. The shock speeds at different cavitation conditions are estimated based on void-fraction measurements using the X-T diagram and compared to those computed using the one-dimensional Rankine Hugoniot jump condition. The two speeds(computed and measured) are found to be comparable. The effect of compressibility of the bubbly mixture is determined by estimating the local speed of sound using homogeneous ‘frozen model’ and homogeneous ‘equilibrium model’. The current estimation of sound speed suggests that expression used to determine the local speed of sound is closer to the classic ‘frozen model’ than the ‘equilibrium model’ of speed of sound.
Osteoporosis is a global public health problem, with fractures contributing to significant morbidity and mortality. Although postmenopausal osteoporosis is most common, up to 30% of postmenopausal ...women, > 50% of premenopausal women, and between 50% and 80% of men have secondary osteoporosis. Exclusion of secondary causes is important, as treatment of such patients often commences by treating the underlying condition. These are varied but often neglected, ranging from endocrine to chronic inflammatory and genetic conditions. General screening is recommended for all patients with osteoporosis, with advanced investigations reserved for premenopausal women and men aged < 50 years, for older patients in whom classical risk factors for osteoporosis are absent, and for all patients with the lowest bone mass (Z-score ≤ -2). The response of secondary osteoporosis to conventional anti-osteoporosis therapy may be inadequate if the underlying condition is unrecognized and untreated. Bone densitometry, using dual-energy x-ray absorptiometry, may underestimate fracture risk in some chronic diseases, including glucocorticoid-induced osteoporosis, type 2 diabetes, and obesity, and may overestimate fracture risk in others (eg, Turner syndrome). FRAX and trabecular bone score may provide additional information regarding fracture risk in secondary osteoporosis, but their use is limited to adults aged ≥ 40 years and ≥ 50 years, respectively. In addition, FRAX requires adjustment in some chronic conditions, such as glucocorticoid use, type 2 diabetes, and HIV. In most conditions, evidence for antiresorptive or anabolic therapy is limited to increases in bone mass. Current osteoporosis management guidelines also neglect secondary osteoporosis and these existing evidence gaps are discussed.
Abstract Bone densitometry (dual energy x-ray absorptiometry-DXA) is a vital medical tool needed for the diagnosis of osteoporosis in non-fractured patients; predicting future fracture risk; and ...monitoring bone mineral density (BMD) in untreated or treated patients. The history of the pivotal international society involved in the science and clinical interpretation of DXA, the International Society for Clinical Densitometry (ISCD) is defined in this manuscript. Since DXA and Osteoporosis management are intimately linked, the ISCD has over the years developed strong bonds with both the National Osteoporosis Foundation (NOF) and the International Osteoporosis Foundation (IOF). The positive impact that ISCD has led in the proper performance and clinical interpretation of bone mass measurements has been enormous worldwide.
The International Society for Clinical Densitometry (ISCD) convened its second Pediatric Position Development Conference (PDC) on October 2-3, 2013 in Baltimore, MD. The conference was co-sponsored ...by the American Society for Bone and Mineral Research (ASBMR) and was held immediately before their annual meeting. The aim of a PDC is to make recommendations for standards in the field of bone densitometry. The recommendations address issues such as quality control, data acquisition and analysis, and the interpretation and reporting of bone densitometric results. In 2007, ISCD convened its first Pediatric PDC to address issues specific to skeletal health assessments in children and adolescents. The 2013 Pediatric PDC focused on advances in the field since that initial conference that would lead to revisions of the original positions. Topics for consideration were developed by the ISCD and its Scientific Advisory Committee. Clinically relevant questions related to each topic were assigned to task forces for a comprehensive review of the medical literature and subsequent presentation of reports to an international panel of experts. Expert panelists included representatives from both the ISCD and ASBMR. The recommendations of the PDC Expert Panel were subsequently reviewed by the ISCD Board of Directors and positions accepted by majority vote. The approved recommendations became the Official Positions of the ISCD. The positions are to be submitted to the ASBMR for its consideration for endorsement. Topics considered at the Pediatric PDC included fracture prediction and definition of osteoporosis, dual-energy X-ray absorptiometry assessment in chronic diseases that may affect the skeleton, dual-energy X-ray absorptiometry interpretation and reporting, quantitative computed tomography measurements, and densitometry in infants and young children. We discuss potential implications of the new recommendations and factors leading to a change in the wording of these positions, considering the science that has evolved over the past 6yr.
Purpose
The purpose of this study is to carry out a comparative study of corneal densitometry (COD) using Pentacam HR in two groups of patients. A control group of normal eyes where corneal pathology ...has been ruled out and another group of patients diagnosed with keratoconus (KC) who have not received corneal Cross‐Linking as treatment.
Methods
The sample consists of 30 eyes diagnosed with keratoconus compared to 30 eyes with normal corneas (N). The results are studied using Pentacam HR, which has a double Scheimpflug chamber. Patients are classified into 2 groups, ruling out corneal pathology in the control group. COD is measured in a 12mm diameter area, divided into concentric annular zones and different depths. COD is used to describe the characteristics of corneal tissue and makes it possible to quantify the degree of transparency of the corneal tissue.
Results
There are significant differences between the groups after the COD examination. In the average of rings and total layers, an increase in total COD is observed in the eyes diagnosed with keratoconus compared to the normal ones (N = 15.71, KC = 21.05). When studied in layers, an increase in densitometry is also seen in the keratoconus group. The front layer (N = 21.61, KC = 29.13), the middle layer (N = 14.49, KC = 18.70) and the back layer (N = 11.04, KC = 14.57).
Conclusions
The corneal densitometry map shows total higher values in eyes with keratoconus compared to healthy eyes. The difference is most marked in the anterior layer of the cornea.
References
1. Maurice DM. The structure and transparency of the cornea. J Physiol. 1957;136:263–286.
2. Shen Y, Han T, Jhanji V, Shang J, Zhao J, Li M, et al. Correlation between corneal topographic, densitometry, and biomechanical parameters in keratoconus eyes. Transl Vis Sci Technol. 2019;8(3):12.
3. Rabinowitz YS. Keratoconus. Surv Ophthalmol. 1998;42(4):297–319.
4. Lopes B, Ramos I, Ambrósio R Jr. Corneal densitometry in keratoconus. Cornea. 2014;33(12):1282–6.
5. Koc M, Tekin K, Tekin MI, Uzel MM, Kosekahya P, Ozulken K, et al. An early finding of keratoconus: Increase in corneal densitometry: Increase in corneal densitometry. Cornea. 2018;37(5):580–6.
The healthy cornea is transparent, however, disease can affect its structure, rendering it more or less opaque. The ability to assess the clarity of the cornea objectively could thus be of ...considerable interest for keratoconus patients. It has previously been suggested that densitometry can be used to diagnose early keratoconus, and that the values of densitometry variables increase with increasing disease severity, indicating that densitometry could also be used to assess progressive keratoconus. Previous studies have only assessed the repeatability of corneal densitometry measurements on the same day, which does not reflect the clinical setting in which changes are evaluated over time. We have therefore evaluated the inter-day repeatability of densitometry measurements in both patients with keratoconus and healthy controls. Measurements in the middle layer of the 2-6 mm zone of the cornea showed the best repeatability. Although an objective measure of the corneal transparency could be interesting, the generally poor repeatability of densitometry measurements limits their use. The repeatability of corneal clarity measurements could be improved by using other approaches such as optical coherence tomography, but this remains to be investigated. Such improvements would allow the more widespread use of corneal densitometry in clinical practice.
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