Microscopic reversibility and emergent elasticity in ultrastable granular systems

In a recent paper (Zhao et al., Phys Rev X, 2022, 12: 031,021), we reported experimental observations of “ultrastable” states in a shear-jammed granular system subjected to small-amplitude cyclic shear. In such states, all the particle positions and contact forces are reproduced after each shear cycle so that a strobed image of the stresses and particle positions appears static. In the present work, we report further analyses of data from those experiments to characterize both global and local responses of ultrastable states within a shear cycle, not just the strobed dynamics. We find that ultrastable states follow a power-law relation between shear modulus and pressure with an exponent β ≈ 0.5, reminiscent of critical scaling laws near jamming. We also examine the evolution of contact forces measured using photoelasticimetry. We find that there are two types of contacts: non-persistent contacts that reversibly open and close; and persistent contacts that never open and display no measurable sliding. We show that the non-persistent contacts make a non-negligible contribution to the emergent shear modulus. We also analyze the spatial correlations of the stress tensor and compare them to the predictions of a recent theory of the emergent elasticity of granular solids, the Vector Charge Theory of Granular mechanics and dynamics (VCTG) (Nampoothiri et al., Phys Rev Lett, 2020, 125: 118,002). We show that our experimental results can be fit well by VCTG, assuming uniaxial symmetry of the contact networks. The fits reveal that the response of the ultrastable states to additional applied stress is substantially more isotropic than that of the original shear-jammed states. Our results provide important insight into the mechanical properties of frictional granular solids created by shear

Elasticity-Controlled Jamming Criticality in Soft Composite Solids

Soft composite solids are made of dispersed inclusions within soft matrices. They are ubiquitous in nature and form the basis of many biological tissues. In the field of materials science, synthetic soft composites are promising candidates for constructing various engineering devices due to their highly programmable features. However, when the volume fraction of inclusions increases, predicting the mechanical properties of these materials poses a significant challenge for the classical theories in composite mechanics. The difficulty arises from the inherently disordered, multi-scale interactions between the inclusions and matrix. To address this challenge, we conducted systematic investigations on the mechanics of densely-filled soft elastomers containing stiff microspheres. We experimentally demonstrated how the strain-stiffening response of the soft composites is governed by the critical scalings in the vicinity of a continuous phase transition, which depend on both the elasticity of the elastomer matrix and the particles. The critical points signify a shear-jamming transition of the included particles in the absence of matrix elasticity. The proposed criticality framework quantitatively predicts diverse mechanical responses observed in experiments across a wide range of material parameters. The findings uncover a novel design paradigm of composite mechanics that relies on engineering the jamming-criticality of the embedded inclusions

Enlightening force chains: a review of photoelasticimetry in granular matter

A photoelastic material will reveal its internal stresses when observed through polarizing filters. This eye-catching property has enlightened our understanding of granular materials for over half a century, whether in the service of art, education, or scientific research. In this review article in honor of Robert Behringer, we highlight both his pioneering use of the method in physics research, and its reach into the public sphere through museum exhibits and outreach programs. We aim to provide clear protocols for artists, exhibit-designers, educators, and scientists to use in their own endeavors. It is our hope that this will build awareness about the ubiquitous presence of granular matter in our lives, enlighten its puzzling behavior, and promote conversations about its importance in environmental and industrial contexts. To aid in this endeavor, this paper also serves as a front door to a detailed wiki containing open, community-curated guidance on putting these methods into practice.Comment: 13 page

Souvenir = Authentic+sustainable : a guide for designers

The designer explores how to improve souvenir design in the real market by questioning the issues of authenticity and the need of sustainable strategies. It takes the city of Växjö as a start point for a touristic place and analyses different categories. Through observations and interviews, the issues are confirmed and a design brief is made. Based on theories of product semantics and emotional design, the result from the investigation summarised to suggest guide for souvenir design. The guide is illustrated in a series of videos meant to anyone working in the souvenir industry

The effect of life events on NSSI: the chain mediating effect of sleep disturbances and PLEs among Chinese college students

This study aimed to explore the relationship between life events and non-suicidal self-injury (NSSI) in college students, as well as the mediating effect of sleep disturbances and psychotic-like experiences (PLEs). After excluding invalid questionnaires, 5,754 were retained, and the valid efficiency was 75.94%. The subjects were aged 16 to 29 years (M = 19.166; SD = 1.392), with 1,969 males (34.22%) and 3,785 females (65.78%). Life events, sleep disturbances, PLEs, and NSSI were assessed using standard scales. Data were analyzed by Pearson Correlation Analysis and bias-correction percentile Bootstrap method. The results show that (1) life events were significant positive predictors of NSSI, sleep disturbances, and PLEs; (2) sleep disturbances, PLEs, and the chain mediation between the two, were mediators between life events and NSSI. Life events are thus shown to be an important external factor influencing NSSI in university students, and this process is mediated through sleep disturbances, PLEs, and the chain between the two. Interventions for NSSI can therefore be made by improving college students’ sleep quality and reducing PLEs

Tuning strain of granular matter by basal assisted Couette shear

We present a novel Couette shear apparatus capable of generating programmable azimuthal strain inside 2D granular matter under Couette shear. The apparatus consists of 21 independently movable concentric rings and two boundary wheels with frictional racks. This makes it possible to quasistatically shear the granular matter not only from the boundaries but also from the bottom. We show that, by specifying the collective motion of wheels and rings, the apparatus successfully generates the desired strain profile inside the sample granular system, which is composed of about 2000 photoelastic disks. The motion and stress of each particle is captured by an imaging system utilizing reflective photoelasticimetry. This apparatus provides a novel method to investigate shear jamming properties of granular matter with different interior strain profiles and unlimited strain amplitudes

The effect of parenting styles on depressive symptoms among Chinese college students: The role of subjective well-being and Taq1A polymorphism

Based on different susceptibility models, the current study constructed a moderated mediation model to explore the influence of parenting style on college students’ depressive symptoms. A total of 301 college students (74 boys and 227 girls) participated in this study. Subjective well-being played a mediating role in the effect of parenting style on depressive symptoms. The DRD2 Taq1A polymorphism moderated the direct pathway in the PPS (positive parenting style) model and the second half of the mediating pathway in the NPS (negative parenting style) model. The findings suggest that the Taq1A polymorphism allele A2 is the plasticity gene for depression, and the A2A2 homozygous gene is the most sensitive to environmental stimuli

Tuning strain of granular matter by basal assisted Couette shear

International audienceWe present a novel Couette shear apparatus capable of generating programmable azimuthal strain inside 2D granular matter under Couette shear. The apparatus consists of 21 independently movable concentric rings and two boundary wheels with frictional racks. This makes it possible to quasistatically shear the granular matter not only from the boundaries but also from the bottom. We show that, by specifying the collective motion of wheels and rings, the apparatus successfully generates the desired strain profile inside the sample granular system, which is composed of about 2000 photoelastic disks. The motion and stress of each particle is captured by an imaging system utilizing reflective photoelasticimetry. This apparatus provides a novel method to investigate shear jamming properties of granular matter with different interior strain profiles and unlimited strain amplitudes