Low Mass Density Research Articles

Flexible and lightweight microcellular RGO@Pebax composites with synergistic 3D conductive channels and microcracks for piezoresistive sensors

Piezoresistive sensors with high flexibility, lightweight and high sensitivity are crucial in variable conductors and wearable devices. Herein, microcellular poly(ether-block-amide) beads coated with reduced graphene oxide (RGO@Pebax) composites with synergistic 3D conductive channels and microcracks were fabricated via the supercritical CO2 foaming followed by dip-coating hydrogen bond assembly, compression moulding and in-situ reduction. The microcellular RGO@Pebax composites exhibit high flexibility (up to 50% compressibility) and low mass density (down to 0.2 g/cm3) due to the incorporation of microcellular structures and 3D interconnected channels. The resultant microcellular RGO@Pebax composites-based piezoresistive sensors exhibit excellent sensing capacity due to the synergistic effect of double mechanisms: “disconnect-connect” transition of microcracks and increased contact area in the 3D conductive channels. Moreover, the piezoresistive sensors exhibit outstanding reliability and stability during the long-term repeated compression strain. Functional applications of the piezoresistive sensors have been demonstrated, indicating their excellent application potentials in variable conductors and wearable devices.

Cardiaovascular Disease Risk Factors in Thai Natural Menopause with First-Time Diagnosis of Low Bone Mass Density

Objective: To evaluate the prevalence of initial cardiovascular disease (CVD) risk factors in naturally postmenopausal Thai women with first-time diagnosis of low bone mass density (BMD), and compare with those reported among general Thai women of the same age range during the same studied time. Methods: A retrospective cross-sectional study of initial CVD risk factors of 473 naturally postmenopausal Thai women (45-60 years) with the first-time diagnosis of osteopenia or osteoporosis without previous treatment for CVD risk factors, except for hypertension(HT) and diabetes mellitus(DM), was performed. Only subjects with all available initial CVD risk factors were recruited. Data included age, weight, height, waist circumference(WC), and underlying diseases. Extracted initial CVD risk factors were: HT, DM, body mass index(BMI), cholesterol level, triglyceride, high density lipoprotein, and family history of CVD. The main outcome was prevalence of initial CVD risk factors with 95%CI. Results were compared with data of previous Thai reports in women of the same age during the same time period. Results: All subjects (86.3% osteopenic, 13.7% osteoporotic) had on average 3.6 years since menopause. Prevalence of women with initial CVD risk factors was 73.8%. The three most common risk factors were high BMI (48.6%), high WC (37.8%) and high cholesterol (22.2%). Only high BMI was more prevalent than previously reported. In contrast, the other factors were lower than previously published data. Conclusion: With the exception of high BMI, initial CVD risk factors in this study were comparable to or lower than those reported in general Thai women of the same age during the same time period.

A flexible phased array system with low areal mass density

Phased arrays are multiple antenna systems capable of forming and steering beams electronically using constructive and destructive interference between sources. They are employed extensively in radar and communication systems but are typically rigid, bulky and heavy, which limits their use in compact or portable devices and systems. Here, we report a scalable phased array system that is both lightweight and flexible. The array architecture consists of a self-monitoring complementary metal–oxide–semiconductor-based integrated circuit, which is responsible for generating multiple independent phase- and amplitude-controlled signal channels, combined with flexible and collapsible radiating structures. The modular platform, which can be collapsed, rolled and folded, is capable of operating standalone or as a subarray in a larger-scale flexible phased array system. To illustrate the capabilities of the approach, we created a 4 × 4 flexible phased array tile operating at 9.4–10.4 GHz, with a low areal mass density of 0.1 g cm^(−2). We also created a flexible phased array prototype that is powered by photovoltaic cells and intended for use in a wireless space-based solar power transfer array.

Free-standing integrated cathode derived from 3D graphene/carbon nanotube aerogels serving as binder-free sulfur host and interlayer for ultrahigh volumetric-energy-density lithium[sbnd]sulfur batteries

The actual applications of lithium sulfur (LiS) batteries are significantly obstructed by limited cyclability and low volumetric-energy-density due to the shuttling effect of polysulfides and low mass density of sulfur cathode. Herein, we report a free-standing, compact, conductive and integrated cathode (G/CNT-S//G/CNT), constructed by compressing graphene/carbon nanotubes (G/CNT) aerogels, simultaneously serving as bi-functionalities of binder- and metal-current-collector-free sulfur host (G/CNT-S) and interlayer (G/CNT), for high volumetric-energy-density LiS batteries. The G/CNT aerogels display three-dimensional interconnected porous network, large surface area (363 m2 g−1) and high electrical conductivity (67 S m−1), which can endow the cathode with ultrahigh volumetric mass density (1.64 g cm−3) and superior electron-ion transport network. Meanwhile, the compressed ultralight G/CNT film can act as flexible interlayer for synergistically suppressing the polysulfide shuttling via both chemical interaction and physical restriction. Consequently, the compact cathodes, achieve high capacity of 1286 mAh g−1 at 0.2 C and long-term cyclability with an extremely low decay rate of 0.06% over 500 cycles at 2 C. Most importantly, our compact cathodes represent unprecedented volumetric capacity of 1841 Ah L−1 and volumetric-energy-density of 2482 Wh L−1, both of which are the highest values of LiS batteries reported to date. Therefore, this proposed strategy will open a new avenue for developing high volumetric-energy-density LiS batteries.

Thermoelectric Figure-of-Merit of Fully Dense Single-Crystalline SnSe.

Single-crystalline SnSe has attracted much attention because of its record high figure-of-merit ZT ≈ 2.6; however, this high ZT has been associated with the low mass density of samples which leaves the intrinsic ZT of fully dense pristine SnSe in question. To this end, we prepared high-quality fully dense SnSe single crystals and performed detailed structural, electrical, and thermal transport measurements over a wide temperature range along the major crystallographic directions. Our single crystals were fully dense and of high purity as confirmed via high statistics 119Sn Mössbauer spectroscopy that revealed <0.35 at. % Sn(IV) in pristine SnSe. The temperature-dependent heat capacity (Cp) provided evidence for the displacive second-order phase transition from Pnma to Cmcm phase at Tc ≈ 800 K and a small but finite Sommerfeld coefficient γ0 which implied the presence of a finite Fermi surface. Interestingly, despite its strongly temperature-dependent band gap inferred from density functional theory calculations, SnSe behaves like a low-carrier-concentration multiband metal below 600 K, above which it exhibits a semiconducting behavior. Notably, our high-quality single-crystalline SnSe exhibits a thermoelectric figure-of-merit ZT ∼1.0, ∼0.8, and ∼0.25 at 850 K along the b, c, and a directions, respectively.

Structure and magnetic properties of cobalt ferrite foam with low mass density

It is extremely desirable but challenging to develop a facile synthesis to directly prepare permanent magnet foam with high coercivity (Hc) and low mass density to meet the requirements of advanced magnets in modern industry. In this work, we developed a facile strategy to synthesize cobalt ferrite foam by solution combustion method and subsequently annealing treatment. The structure and magnetic properties of the foams can be influenced by the ratios of glycine to nitrate (G/N), Co content and annealing treatment temperatures. The increase in the mean grain sizes within the single domain range gives rise to an enhancement in coercivities. The highest Hc of ∼3 kOe with an ultra-low mass density of ∼45 mg/cm3 can be successfully obtained by controlling the preparation process. The work opens up a new way to prepare ultra-light Fe-based oxides for magnetic and catalytic applications.

Are Skeletal Muscle Mass and Density Associated with Fatigue In Early-Stage Colorectal Cancer Patients?

Abstract Both low skeletal muscle mass and low radiographic muscle density are associated with higher complication rates after surgery for colorectal cancer and with worse survival rates although data are not fully consistent. Whether skeletal muscle mass and density are also associated with patient-reported outcomes, such as fatigue, is less well studied. We hypothesized that low skeletal muscle mass and density may be associated with fatigue in early stage colorectal cancer (CRC) patients. Methods: Within a prospective cohort of 594 early-stage (stage I-III) CRC patients, we collected information on fatigue using the EORTC QLQ-C30 questionnaire 6 months after diagnosis; fatigue was defined as a score of &amp;gt;39 based on literature. Skeletal muscle mass and -density were assessed using pre-operative Computed Tomography (CT) images. Low muscle mass and -density were identified using previously determined cut- off values. Cox regression models were used to calculate prevalence ratios (PRs). All PRs were adjusted for age, sex, stage of disease. Results: The average age of the study population was 65.7 ± 9.0; 37% were women and 67% of the patients had a tumor located in the colon. Low muscle mass was present in 26% of the patients and low muscle density in 25%; 26% of patients had fatigue. Low muscle mass was not associated with prevalence of fatigue (PR for low versus normal muscle mass 0.83 (95%CI 0.56–1.24). Low muscle density was associated with higher prevalence of fatigue: PR for low versus normal muscle density 1.94 (95% CI 1.34–2.81). Conclusion: Among colorectal cancer patients, low skeletal muscle density at diagnosis - indicative for fat infiltration in the muscle- was associated with a higher prevalence of fatigue six months after diagnosis. Future studies should assess how lifestyle interventions can help to prevent or decrease fatigue, and should further clarify whether there is a causal link between fat infiltration in the muscle and fatigue.

Role of Bisphosphonate Therapy in Patients with Osteopenia: A Systemic Review.

By contrast to clinical trials exploring osteoporosis, clinical trials specifically designed for the osteopenic population are limited. Thus, less clinical data are available regarding treatment benefits and cost-effectiveness of treating a patient population with a bone mass density in the osteopenic range (T-score between -1 and -2.5). In this article, we aimed to highlight this high-risk population with a low bone mass density (BMD) susceptible to high fracture risk by reviewing different national and international guidelines for treating osteopenia. The cost-effectiveness of the therapy for the above-mentioned patient population is also discussed. By reviewing different clinical trials, we have specifically highlighted the role of bisphosphonate therapy for fracture risk reduction and increment in bone mineral density (BMD) in patients with osteopenia.

Low lattice thermal conductivity and high thermoelectric figure of merit in Na2MgSn

Thermoelectric materials enables the harvest of waste heat and directly conversion into electricity. In search of high efficient thermoelectric materials, low thermal conductivity of a material is essential and critical. Here, we have theoretically investigated the lattice thermal conductivity and thermoelectric properties of layered intermetallic Na$_2$MgSn and Na$_2$MgPb based on the density functional theory and linearized Boltzmann equation with the single-mode relaxation-time approximation. It is found that both materials exhibit very low and anisotropic intrinsic lattice thermal conductivity. Despite of the very low mass density and simple crystal structure of Na$_2$MgSn, its lattice thermal conductivities along $a$ and $c$ axes are only 1.75 and 0.80 W/m$\cdot$K respectively at room temperatures. When Sn is replaced by the heavier element Pb, its lattice thermal conductivities decrease remarkably to 0.51 and 0.31 W/m$\cdot$K respectively along $a$ and $c$ axes at room temperatures. We show that the low lattice thermal conductivities of both materials are mainly due to their very short phonon lifetimes, which are roughly between 0.4 to 4.5 ps. Combined with previous experimental measurements, the metallic Na$_2$MgPb can not be a good thermoelectric material. However, we predict that the semiconducting Na$_2$MgSn is a potential room-temperature thermoelectric material with a considerable $ZT$ of 0.34 at 300 K. Our calculations not only imply that the intermetallic Na$_2$MgSn is a potential thermoelectric material, but also can motivate more theoretical and experimental works on the thermoelectric researches in simple layered intermetallic compounds.

Status of bone health and association of socio-demographic characteristics with Bone Mineral Density in Pakistani Females.

Background & Objective:The “silent thief” of bone osteoporosis is associated with various modifiable factors, identifying these factors is important in decreasing the prevalence of this highly prevalent disease. Therefore, this study was planned to identify these risk factors for osteoporosis in premenopausal and postmenopausal Pakistani women.Methods:A total of 1205 pre and postmenopausal females between the ages of 20 to 80 years were selected. Detailed history about the socio-demographic characteristics including age, education, profession, marital and resident status was recorded. Medical and gynecological history was also taken after informed consent Bone health of females was assessed using calcaneal ultrasound bone densitometer. SPSS 22.0 was used to analyze data.Results:Univariate analysis showed that age (30-39 yrs, and 60-69 yrs), occupation (housewives) and education (secondary and primary education, illiterate) were significantly associated with low bone mass density (LBMD). Multivariate analysis showed that age 30-39 years (OR=0.25 95%CI 0.13 – 0.49), age 40-49 years (OR=0.30 95%CI 0.15 – 0.59), age 50-59 years (OR=0.42 95%CI 0.22 – 0.79), primary education (OR=3.83, 95%CI 2.30 - 6.38) and illiteracy (OR=3.83 95%CI 2.52 – 5.82), were significantly associated with LBMD. The prevalence of osteopenia and osteoporosis was 29.8%, 27.2%, respectively, while 43% subjects had normal BMD.Conclusion:It is concluded that, within Pakistani population, the prevalence of osteopenia is high even at an early age group and the odds of having LBMD are more in less educated or illiterate women.

Brzine čestica praha u plazmi na niskom pritisku

Low pressure of inert gas in the vacuum chamber significantly affects the transfer of plasma particle velocity onto powder particles, residence time of powder particles in plasma and the kinetic energy of molten particles before the collision with the substrate. In addition to low pressure of inert gas in the vacuum chamber, the size and mass density of powder particles, together with plasma arc power, have the biggest impact on the average velocity of powder particles. To measure the velocity of powder particles in the vacuum chamber at low pressure, a laser speedometer is applied.The average velocity of molten powder particles V=s/t is calculated when the length of the path of powder particles that pass between two focus distances of the laser beam is divided by the time of particle passage between the two focuses. Measurements are done for vacuum chamber pressure, the values of which are usually from 6.7 to 80 kPa. The paper describes the relationship between the average velocity of Al2O3 and W powder particles and the vacuum chamber pressure, granulate distribution, mass density and plasma arc power. It was found that, for powder of lower mass density, the average velocity of particles can increase for 200 m/s with a decrease in chamber pressure.The effect of pressure on W particles of larger mass density is lower but still important, because a decrease in pressure increases the average velocity of particles up to 50%. Reducing plasma arc power reduces the maximum velocity of both types of powder particles. .

A Fast Response-Recovery 3D Graphene Foam Humidity Sensor for User Interaction.

Humidity sensors allow electronic devices to convert the water content in the environment into electronical signals by utilizing material properties and transduction techniques. Three-dimensional graphene foam (3DGF) can be exploited in humidity sensors due to its convenient features including low-mass density, large specific surface area, and excellent electrical. In this paper, 3DGF with super permeability to water enables humidity sensors to exhibit a broad relative humidities (RH) range, from 0% to 85.9%, with a fast response speed (response time: ~89 ms, recovery time: ~189 ms). To interpret the physical mechanism behind this, we constructed a 3DGF model decorated with water to calculate the energy structure and we carried out the CASTEP as implemented in Materials Studio 8.0. This can be ascribed to the donor effect, namely, the electronic donation of chemically adsorbed water molecules to the 3DGF surface. Furthermore, this device can be used for user interaction (UI) with unprecedented performance. These high performances support 3DGF as a promising material for humidity sensitive material.

Flexible and stable high-energy lithium-sulfur full batteries with only 100% oversized lithium

Lightweight and flexible energy storage devices are urgently needed to persistently power wearable devices, and lithium-sulfur batteries are promising technologies due to their low mass densities and high theoretical capacities. Here we report a flexible and high-energy lithium-sulfur full battery device with only 100% oversized lithium, enabled by rationally designed copper-coated and nickel-coated carbon fabrics as excellent hosts for lithium and sulfur, respectively. These metallic carbon fabrics endow mechanical flexibility, reduce local current density of the electrodes, and, more importantly, significantly stabilize the electrode materials to reach remarkable Coulombic efficiency of >99.89% for a lithium anode and >99.82% for a sulfur cathode over 400 half-cell charge-discharge cycles. Consequently, the assembled lithium-sulfur full battery provides high areal capacity (3 mA h cm−2), high cell energy density (288 W h kg−1 and 360 W h L−1), excellent cycling stability (260 cycles), and remarkable bending stability at a small radius of curvature (<1 mm).

Relationship between serum level of growth differentiation factors 8, 11 and bone mineral density in girls with anorexia nervosa.

Adolescents with anorexia nervosa (AN) have low body mass and low bone mineral density (BMD). Growth differentiation factor 8 (Myostatin, GDF8) and its homologue growth differentiation factor 11 (GDF11), members of the TGF-β super-family, play an important role in muscle regeneration and bone metabolism in healthy individuals. However, their association with BMD in AN is unknown. The present study was undertaken to investigate the relationship between GDF8, GDF11 and BMD in adolescent girls with AN. Serum GDF8, GDF11 and BMD were determined in 25 girls (12-16years old) with AN and 31 healthy girls (12-16years old). Growth differentiation factor 8 levels were lower in AN subjects. On the contrary, GDF11 levels were higher in AN subjects than controls. There was no relationship between GDF8 and BMD. A significant negative correlation between GDF11 and BMD was found. In multiple linear stepwise regression analysis, BMI, 25-hydroxyvitamin D, GDF11, or lean mass, but not fat mass and GDF8, were independent predictors of BMD in the AN and control groups separately. Growth differentiation factor 11 was independent predictor of BMD in girls with AN. It suggested that GDF11 exerts a negative effect on bone mass.

Three-dimensional pentagonal silicon: Stability and properties

Motivated by the compatibility with the well-developed Si-based semiconductor technology, research on new Si allotropes is of importance. Here, we study a new three-dimensional (3D) silicon (named as pentagonal-Si), which is entirely composed of pentagons with all atoms in sp3-hybridized states. State-of-the-art theoretical calculations confirm that the new silicon phase is dynamically, thermally and mechanically stable. The calculations of electronic band structure with HSE06 functional show that pentagonal-Si is a semiconductor with an indirect band gap of 2.05 eV that is much larger than that of diamond-Si, leading to distinguished optical absorption. Moreover, pentagonal-Si has a lower mass density (2.09 g/cm3) compared with diamond-Si (2.34 g/cm3), and exhibits a higher carrier mobility (∼3 × 103 cm2/V·s) at ambient temperature, adding new feature for optoelectronic applications.

Pre-operative muscle density and not muscle mass is associated with overall mortality in early-stage colorectal cancer patients

Rationale: In cancer patients with a relatively poor prognosis, both low skeletal muscle mass and low skeletal muscle density are thought to be associated with higher mortality. Whether these associations also hold for earlier stage cancer is less clear. We aimed to study the association between muscle mass, density and overall mortality among early-stage (stage I-III) colorectal cancer (CRC) patients with a relatively good prognosis.

Outer Solar System Possibly Shaped by a Stellar Fly-by

The planets of our solar system formed from a gas-dust disk. However, there are some properties of the solar system that are peculiar in this context. First, the cumulative mass of all objects beyond Neptune (TNOs) is only a fraction of what one would expect. Second, unlike the planets themselves, the TNOs do not orbit on coplanar, circular orbits around the Sun, but move mostly on inclined, eccentric orbits and are distributed in a complex way. This implies that some process restructured the outer solar system after its formation. However, some of TNOs, referred to as Sednoids, move outside the zone of influence of the planets. Thus external forces must have played an important part in the restructuring of the outer solar system. The study presented here shows that a close fly-by of a neighbouring star can simultaneously lead to the observed lower mass density outside 30 AU and excite the TNOs onto eccentric, inclined orbits, including the family of Sednoids. In the past it was estimated that such close fly-bys are rare during the relevant development stage. However, our numerical simulations show that such a scenario is much more likely than previously anticipated. A fly-by also naturally explains the puzzling fact that Neptune has a higher mass than Uranus. Our simulations suggest that many additional Sednoids at high inclinations still await discovery, perhaps including bodies like the postulated planet X.

Two-dimensional materials: Emerging toolkit for construction of ultrathin high-efficiency microwave shield and absorber

Two-dimensional (2D) materials generally have unusual physical and chemical properties owing to the confined electro-strong interaction in a plane and can exhibit obvious anisotropy and a significant quantum-confinement effect, thus showing great promise in many fields. Some 2D materials, such as graphene and MXenes, have recently exhibited extraordinary electromagnetic-wave shielding and absorbing performance, which is attributed to their special electrical behavior, large specific surface area, and low mass density. Compared with traditional microwave attenuating materials, 2D materials have several obvious inherent advantages. First, similar to other nanomaterials, 2D materials have a very large specific surface area and can provide numerous interfaces for the enhanced interfacial polarization as well as the reflection and scattering of electromagnetic waves. Second, 2D materials have a particular 2D morphology with ultrasmall thickness, which is not only beneficial for the penetration and dissipation of electromagnetic waves through the 2D nanosheets, giving rise to multiple reflections and the dissipation of electromagnetic energy, but is also conducive to the design and fabrication of various well-defined structures, such as layer-by-layer assemblies, core–shell particles, and porous foam, for broadband attenuation of electromagnetic waves. Third, owing to their good processability, 2D materials can be integrated into various multifunctional composites for multimode attenuation of electromagnetic energy. In addition to behaving as microwave reflectors and absorbers, 2D materials can act as impedance regulators and provide structural support for good impedance matching and setup of the optimal structure. Numerous studies indicate that 2D materials are among the most promising microwave attenuation materials. In view of the rapid development and enormous advancement of 2D materials in shielding and absorbing electromagnetic wave, there is a strong need to summarize the recent research results in this field for presenting a comprehensive view and providing helpful suggestions for future development.

Experimental study of expanded cork agglomerate blocks – Compressive creep behavior and dynamic performance

The main goal of the present work is to experimentally evaluate the behavior of expanded cork agglomerate blocks subjected to static and dynamic loads. The study focuses on the compressive and creep effects and on the vibration isolation capability.First, compressive creep behavior and deformation recovery capability (after loading) tests were performed on blocks made of expanded cork agglomerate. The dynamic characterization then involved performing transmissibility tests for different static and dynamic loading conditions and evaluating the dynamic transfer stiffness and damping ratio of the blocks. The resulting transmissibility curves indicate how much vibration is transmitted through the isolator to its base at a given frequency. These tests were also performed under different conditions of strain to better understand the effect on the dynamic performance of the material, and to assess whether it might be a limiting factor.The results show that expanded cork agglomerate blocks, especially those with higher mass density, have physical and mechanical properties that provide this material with great potential for withstanding heavy static loads since small compressive creep effects and low permanent deformation was exhibited.The results also indicate that expanded cork agglomerate can be a good option for mitigating vibration. It was found that specimens with lower mass density and larger thickness performed better, with higher vibration isolation and a wider range of frequencies isolated. However, this behavior is limited by the influence of compressive stress on the blocks.

VZLUSAT‐1: Health monitoring system, preliminary results

The health monitoring (HM) system placed on VZLUSAT‐1 nondestructively measures the mechanical and thermal properties of the newly developed carbon fiber material for space usage. The carbon material is exposed to the vacuum, radiation, and temperature changes in space. It can be used as a substitute for the currently used aluminum alloys because it has lower mass density and better mechanical properties compared to aluminum. The HM payload evaluates the quality changes of a material according to the difference in Young's modulus. Young's modulus of elasticity is a characteristic property of every solid material, and on VZLUSAT‐1 it is measured in terms of the eigenfrequencies of a free‐hanging beam. In this paper we present the first data measured in orbit – the eigenfrequencies, attenuation, and six temperatures from a carbon fiber panel. Based on these data, the quality of the mechanical properties and time stability are determined over the VZLUSAT‐1's life span.