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Particle shape is a key to the space-filling and strength properties of granular matter. We consider a shape parameter η describing the degree of distortion from a perfectly spherical shape. Encompassing most specific shape characteristics such as elongation, angularity and non-convexity, η is a low-order but generic parameter that we used in a numerical benchmark test for a systematic investigation of shape dependence in sheared granular packings composed of particles of different shapes. We find that the shear strength is an increasing function of η with nearly the same trend for all shapes, the differences appearing thus to be of second order compared to η. We also observe a non-trivial behavior of packing fraction which, for all our simulated shapes, increases with η from the random close packing fraction for disks, reaches a peak considerably higher than that for disks, and subsequently declines as η is further increased. These findings suggest that a low-order description of particle shape accounts for the principal trends of packing fraction and shear strength. Hence, the effect of second-order shape parameters may be investigated by considering different shapes at the same level of η. [ABSTRACT FROM AUTHOR]

We use three-dimensional contact dynamics simulations to analyze the rheological properties of granular materials composed of rigid aggregates. The aggregates are made from four overlapping spheres and described by a nonconvexity parameter depending on the relative positions of the spheres. The macroscopic and microstructural properties of several sheared packings are analyzed as a function of the degree of nonconvexity of the aggregates. We find that the internal angle of friction increases with the nonconvexity. In contrast, the packing fraction first increases to a maximum value but declines as the nonconvexity increases further. At a high level of nonconvexity, the packings are looser but show a higher shear strength. At the microscopic scale, the fabric and force anisotropy, as well as the friction mobilization, are enhanced by multiple contacts between aggregates and interlocking, thus revealings the mechanical and geometrical origins of shear strength.

The macroscopic cohesion of granular materials made up of sticky particles depends on the particle shapes. We address this issue by performing contact dynamics simulations of 2D packings of nonconvex aggregates. We find that the macroscopic cohesion is strongly dependent on the strain and stress inhomogeneities developing inside the material. The largest cohesion is obtained for nearly homogeneous deformation at the beginning of unconfined axial compression and it evolves linearly with nonconvexity. Interestingly, the aggregates in a sheared packing tend to form more contacts with fewer neighboring aggregates as the degree of nonconvexity increases. We also find that shearing leads either to an isotropic distribution of tensile contacts or to the same privileged direction as that of compressive contacts.

The objectives of these incisions are: in the temporal region to preserve hair capital and to elevate the temporo-canthal region while keeping side burns in place--this "Z" type incision is particularly useful for mak life surgery--in the mastoïde region, to minimize common "step" in hairline and to have a good lift effect even in the back part of this short incision. The oblique SMAS flap begins 2 cm under the canthal region and finishes in the neck at the posterior border of the plastysma muscle. The posterior border of the flap is thus close and parallel to the medial folds of the face. The suture of this border after ascension of the flap ensures good results on these ageing folds. The subsmas dissection of the malar region allows lifting of the sliding malar fat pad. The submalar crease disappears and the nasolabial fold is improved.

The subperiosteal facelift is, as its name indicates, a deep technique essentially adapted to the upper two-thirds of the face. It is performed via a bicoronal incision, often associated with a vestibular incision, which allows frontal, maxillary, malar, zygomatic and orbital dissection. Section of the superficial leaflet of the temporal aponeurosis reveals the DMAS (Deep Musculo Aponeurotic System) which can be used to raise all of the soft tissues of the face while protecting the frontal branch of the facial nerve. Elevation of the tissues of the face is essentially vertical and acts on the forehead, temporal region, gaze and cheekbones. Current incisions allow maximal preservation of hair and avoid ascension of the sideburns. This technique is particularly indicated in relatively young subjects.

The subperiosteal lift developed by Tessier is a technique for rejuvenating the face and emphasizing beauty. It is performed using two approaches: intraoral and bicoronal or precapillary. It entails a total subperiosteal undermining of the face beginning 2 cm over the orbits and continuing on the orbital rims, the zygomatic arches, and the malar bones. This allows total lifting of the soft tissues of the face (DMAS, deep musculo aponeurotic system). The lateral and vertical traction allows elevation of the superior two thirds of the face, eyebrows, and cheeks. Lifting pulls up from the forehead to the mandibular line. The fixation of the superficial layer of the temporal aponeurosis in traction to the upper part also has an effect on tissue elevation. The best candidates for this procedure are women in their late 30s or early 40s but can be used on those from 30 to 50 and more. It is highly specialized operation which requires substantial surgical experience both in selecting the patient and in execution.

The lower eyelid consists of four planes. The deepest plane is the orbital fat, followed by the septum, orbicularis muscle and the skin. Pouches are classically treated by resection of the fat, i.e. reduction of the orbital contents De La Plazza proposed a new method by tightening the septum which retains the orbital fat posteriorly. This idea of preservation of the orbital fat led me to consider the third plane: the orbicularis muscle. By comparing orbicularis myorraphy with median myorraphy of abdominal plasties. I propose reinforcement of the orbicularis muscle to retain the orbital fat and to reduce the pouches without resection of the fat. The fourth plane, the skin, is classically draped over the muscular layer, but as the height of the muscle plane is reduced by this myorraphy, this skin will be less involved in smiling, which improves the wrinkles. As the skin is traditionally detached from the muscle, autoplication of the orbicularis muscle is performed, taking care not to modify the position of the free edge in order not to create muscular ectropion. This suture is composed of inverted 6/0 Dexon sutures. The advantages are preservation of the orbicularis fat which prevents loss of this fat and the risk of senile enophthalmia in the long-term. The indications are of three orders: a) pouches when they are not excessive; b) static wrinkles; c) dynamic wrinkles of smiling. A muscular roll must be avoided by a very careful suture technique. Orbicularis myorraphy appears to be a new contribution to the various therapeutic procedures proposed for aesthetic blepharoplasty and may improve some of the results.