Millennial-scale migration of the frozen/melted basal boundary, western Greenland ice sheet

The geometry and thermal structure of western Greenland ice sheet are known to have undergone relatively substantial change over the Holocene. Evolution of the frozen and melted fractions of the bed associated with the ice-sheet retreat over this time frame remains unclear. We address this question using a thermo-mechanically coupled flowline model to simulate a 11 ka period of ice-sheet retreat in west central Greenland. Results indicate an episode of ~100 km of terminus retreat corresponded to ~16 km of upstream frozen/melted basal boundary migration. The majority of migration of the frozen area is associated with the enhancement of the frictional and strain heating fields, which are accentuated toward the retreating ice margin. The thermally active bedrock layer acts as a heat sink, tending to slow contraction of frozen-bed conditions. Since the bedrock heat flux in our region is relatively low compared to other regions of the ice sheet, the frozen region is relatively greater and therefore more susceptible to marginward changes in the frictional and strain heating fields. Migration of melted regions thus depends on both geometric changes and the antecedent thermal state of the bedrock and ice, both of which vary considerably around the ice sheet.

The Irradiation Instability of Protoplanetary Disks

The temperature in most parts of a protoplanetary disk is determined by irradiation from the central star. Numerical experiments of Watanabe and Lin suggested that such disks, also called “passive disks,” suffer from a thermal instability. Here we use analytical and numerical tools to elucidate the nature of this instability. We find that it is related to the flaring of the optical surface, the layer at which starlight is intercepted by the disk. Whenever a disk annulus is perturbed thermally and acquires a larger scale height, disk flaring becomes steeper in the inner part and flatter in the outer part. Starlight now shines more overhead for the inner part and so can penetrate into deeper layers; conversely, it is absorbed more shallowly in the outer part. These geometric changes allow the annulus to intercept more starlight, and the perturbation grows. We call this the irradiation instability. It requires only ingredients known to exist in realistic disks and operates best in parts that are both optically thick and geometrically thin (inside 30 au, but can extend to further reaches when, e.g., dust settling is considered). An unstable disk develops traveling thermal waves that reach order unity in amplitude. In thermal radiation, such a disk should appear as a series of bright rings interleaved with dark shadowed gaps, while in scattered light it resembles a moving staircase. Depending on the gas and dust responses, this instability could lead to a wide range of consequences, such as ALMA rings and gaps, dust traps, vertical circulation, vortices, and turbulence.

A flexible electronic strain sensor for the real-time monitoring of tumor progression

Healthcare professionals and scientists utilize tumor shrinkage as a key metric to establish the efficacy of cancer treatments. However, current measurement tools such as CT scanners and calipers only provide brief snapshots of the dynamic geometric changes occurring in vivo, and they are unable to detect the micrometer-scale volumetric transformations transpiring at minute timescales. Here we present a stretchable electronic strain sensor, with a 10-micron scale resolution, capable of continuously monitoring tumor volume progression in real-time. In mouse models with subcutaneously implanted lung cancer or B-cell lymphoma tumors our sensors discerned a significant change in the tumor volumes of treated mice within 5 hours after small molecule therapy or immunotherapy initiation. Histology, caliper measurements, and luminescence imaging over a one-week treatment period validated the data from the continuous sensor. We anticipate that real-time tumor progression datasets could help expedite and automate the process of screening cancer therapies in vivo.

Social And Medical Aspects Of Left Ventricular Diastolic Dysfunction In Arterial Hypertension

Chronic heart failure (CHF) is a syndrome of several chronic diseases of the cardiovascular system. Among them, arterial hypertension (AH) occupies an important place. High blood pressure (BP) is considered to be the most common cause of CHF. The progression of hypertension towards heart failure includes geometric changes in LV and DD.

Testing of mechanical butt joints in composite structures

As the main contribution of the present study, an I-shaped joining element, which allows the plates used in large composite structures to be joined butt-to-butt, has been improved in terms of load capabilities. It is desirable that the joining zones of composite plates not be visible according to the design of composite structures and the requirements for the desired use in particular. In other words, it is not desirable to create any surfaces that would cause protrusions in the joining zones. The only joining technique that fulfils this condition is the butt joint. Generally, butt joints are performed by bonding. With this technique, it is possible to make a more durable mechanical butt joint using an I-shaped joining element. In this way, instead of bonding butt joints, stronger non-bonding or bonding mechanical butt joints can also be achieved. In this study, the geometric changes in the shape of an I-shaped joining element used in mechanical butt joints and the changes in load-carrying capabilities have been studied experimentally and numerically. Experiments were carried out with tensile, three-point bending and four-point bending tests. The experimental specimens and I-shaped joining elements were cut using a water jet machine. Abaqus finite element analysis software was used for numerical analysis. The numerical data obtained in the study were found to be consistent with the experimental data. The load-carrying capabilities of the joining elements of different geometric shapes were studied numerically and experimentally, and it was found that the ideal element was the joining element with a 60° angle.

Blood Pressure and Left Ventricular Geometric Changes: A Directionality Analysis

This study assessed the temporal relationship of elevated blood pressure (BP) with left ventricular hypertrophy (LVH) and geometric changes in a longitudinal cohort of adults. Left ventricular mass index (LVMI), relative wall thickness (RWT), and BP were measured at 2 time points 4.1 to 14.9 years apart between 2000 and 2016 among 984 adults (677 White and 307 Black people; 41.1% men; age range, 24.2–56.7 years) in the Bogalusa Heart Study cohort. Cross-lagged path analysis models were used to examine the temporal relationship of BP with LVMI and RWT in subjects who did not take antihypertensive medications (n=693). The cross-lagged path coefficients did not differ significantly between race and sex groups. In the combined sample, the path coefficients from baseline systolic BP to follow-up LVMI/RWT were significantly greater than the path coefficients from baseline LVMI/RWT to follow-up systolic BP (0.111 versus −0.005 for LVMI, P =0.010 for difference; 0.146 versus 0.004 for RWT, P =0.002 for difference). Hypertensive subjects at baseline had a significantly higher incidence rate of concentric LVH at follow-up compared with normotensive subjects (19.4% versus 9.7%, P <0.001 for difference), but incident eccentric LVH did not show such a difference between hypertensive and normotensive subjects (5.4% versus 4.4%, P =0.503 for difference). Diastolic BP showed similar results to those of systolic BP. In conclusion, the findings on these one-directional paths provide strong and fresh evidence that elevated BP precedes the development of LVH, especially concentric LVH, during the young-to-midlife adult age period.

Systemic Modeling of Chaotic EEG During Human Sleep

One of the most challenging discussions about EEG is the chaotic nature of this biological signal. In the present study, we attempt to provide an analysis to demonstrate sleep EEG chaoticity. We model changes of sleep attractor dynamic in phase space by exponential regression. Our model demonstrates that the sleep attractor is the sleep cycle attractor whose size shrinks during successive cycles by presenting a new definition of the sleep cycle. We study the EEG dynamics of different sleep stages by presenting two new features based on phase space properties. We show that each stage has a unique chaotic attractor. We model geometric changes of these attractors during successive sleep cycles. Our model achieves an accuracy, sensitivity, and specificity of 89.15%, 82.84%, and 81.62% classifying sleep stages.

Geometric changes in aortic root replacement using Freestyle prosthesis

Background The Medtronic Freestyle prosthesis has proven to be a promising recourse for aortic root replacement in various indications. The present study aims to evaluate clinical outcomes and geometric changes of the aorta after Freestyle implantation. Methods Between October 2005 and November 2020, the computed tomography angiography (CTA) data of 32 patients were analyzed in a cohort of 68 patients that underwent aortic root replacement using Freestyle prosthesis. The minimum and maximum diameters and areas of the aortic annulus, aortic root, ascending aorta, and the proximal aortic arch were measured at a plane perpendicular to the long axis of the aorta using 3D multiplanar reconstruction in both the preoperative (n = 32) and postoperative (n = 10) CTAs. Moreover, volumetric changes of the aortic root and ascending aorta were quantified. Results Mean age was 64.6 ± 10.6 years. Indications for surgery using Freestyle prosthesis were combined aortic valve pathologies, aortic aneurysm or dissection, and endocarditis, with concomitant surgery occurring in 28 out of 32 patients. In-hospital mortality was 18.6%. Preoperative diameter and area measurements of the aortic annulus strongly correlated with the implanted valve size (p < 0.001). Bicuspid valve was present in 28.1% of the patients. Diameter and areas of the aortic root decreased after freestyle implantation, resulting in a reduction of the aortic root volume (45.6 ± 26.3 cm3 to 18.7 ± 4.5 cm3, p = 0.029). Volume of the aortic root and the ascending aorta decreased from 137.3 ± 65.2 cm3 to 54.5 ± 21.1 cm3 after Freestyle implantation (p = 0.023). Conclusion Implantation of the Freestyle prosthesis presents excellent results in restoring the aortic geometry. Preoperative CTA measurements are beneficial to the surgical procedure and valve selection and therefore, if available, should be considered in pre-operative planning.

Changes in the three-dimensional microscale topography of human skin with aging impact its mechanical and tribological behavior

Human skin enables interaction with diverse materials every day and at all times. The ability to grasp objects, feel textures, and perceive the environment depends on the mechanical behavior, complex structure, and microscale topography of human skin. At the same time, abrasive interactions, such as sometimes occur with prostheses or textiles, can damage the skin and impair its function. Previous theoretical and computational efforts have shown that skin’s surface topography or microrelief is crucial for its tribological behavior. However, current understanding is limited to adult surface profiles and simplified two-dimensional simulations. Yet, the skin has a rich set of features in three dimensions, and the geometry of skin is known to change with aging. Here we create a numerical model of a dynamic indentation test to elucidate the effect of changes in microscale topography with aging on the skin’s response under indentation and sliding contact with a spherical indenter. We create three different microrelief geometries representative of different ages based on experimental reports from the literature. We perform the indentation and sliding steps, and calculate the normal and tangential forces on the indenter as it moves in three distinct directions based on the characteristic skin lines. The model also evaluates the effect of varying the material parameters. Our results show that the microscale topography of the skin in three dimensions, together with the mechanical behavior of the skin layers, lead to distinctive trends on the stress and strain distribution. The major finding is the increasing role of anisotropy which emerges from the geometric changes seen with aging.