Dynamics of book sales: endogenous versus exogenous shocks in complex networks.

We present an extensive study of the foreshock and aftershock signatures accompanying peaks of book sales. The time series of book sales are derived from the ranking system of Amazon.com. We present two independent ways of classifying peaks, one based on the acceleration pattern of sales and the other based on the exponent of the relaxation. They are found to be consistent and reveal the coexistence of two types of sales peaks: exogenous peaks occur abruptly and are followed by a power law relaxation, while endogenous sale peaks occur after a progressively accelerating power law growth followed by an approximately symmetrical power law relaxation which is slower than for exogenous peaks. We develop a simple epidemic model of buyers connected within a network of acquaintances which propagates rumors and opinions on books. The comparison between the predictions of the model and the empirical data confirms the validity of the model and suggests in addition that social networks have evolved to converge very close to criticality (here in the sense of critical branching processes of opinion spreading). We test in detail the evidence for a power law distribution of book sales and confirm a previous indirect study suggesting that the fraction of books (density distribution) P (S) of sales S is a power law P(S) approximately 1/ S(1+mu) with mu approximately equal to 2 .

Endogenous versus exogenous shocks in complex networks: an empirical test using book sale rankings.

We study the precursory and recovery signatures accompanying shocks in complex networks, that we test on a unique database of the Amazon.com ranking of book sales. We find clear distinguishing signatures classifying two types of sales peaks. Exogenous peaks occur abruptly and are followed by a power law relaxation, while endogenous peaks occur after a progressively accelerating power law growth followed by an approximately symmetrical power law relaxation which is slower than for exogenous peaks. These results are rationalized quantitatively by a simple model of epidemic propagation of interactions with long memory within a network of acquaintances. The observed relaxation of sales implies that the sales dynamics is dominated by cascades rather than by the direct effects of news or advertisements, indicating that the social network is close to critical.

[A new procedure for fragmenting the lens with soft-edge micromanipulation during phacoemulsification]. / Nouveau procédé pour fendre le cristallin à l'aide de micromanipulateurs à bords mousses au cours de la phakoémulsification.

During phacoemulsification: Presentation of a new method of manual nucleofracture performed with the use of small-volume and soft-edge micromanipulators. This method presents several advantages: During the last three years 1200cataract operations have been performed without capsulor rupture and without durable endothelial damage.

[Long-term results of trabeculectomy]. / Résultats à long terme de la trabéculectomie.

We have studied 93 cases of trabeculectomy, most of them performed on primary chronic open angle glaucomas, with a follow up of 2 to 11 years. Reviewing of the results point out that intraocular pressure stabilization over a long time period is correlated to the existence of an effective subconjunctival filtering bleb. Recurrence of hypertension increases with time, but most of the cases are stabilized by medical treatment, or by laser trabeculoplasty, when it is possible. Cataract producing concerns 46% of the cases, happening within one to three years in most of them. It is greatly influenced by patients age. On the other hand, effective subconjunctival filtering bleb and transient post operative athalamy are not major factors.

[Malignant hemangioendothelioma of the choroid]. / Hémangio-endothéliome malin de la choroïde.

The authors report the case of a malignant hemangioendothelioma of the choroid occurred in a 62 years old man. Clinically the lesion simulated a malignant melanoma but the histological examination showed an unpigmented tumour consisting of nests of large, pleomorphic cells proliferating inside reticular sheaths. The immunohistochemical identification of Factor VIII Related Antigen by the peroxidase-antiperoxidase method of Sternberger permitted the identification of their endothelial nature. This case which seems to be the first described in the literature, is distinguished from benign hemangioendothelioma and from neoplastic angioendotheliomatosis.

[Comments based on 256 intraocular implants placed after extracapsular extraction of the crystalline lens]. / Réflexions après 256 implants intraoculaires mis en place après extraction extracapsulaire du cristallin.

Results of 256 intraocular lens implants after extracapsular cataract extraction are analysed with a mean follow-up period of four years. Different models of intraocular lenses were used: mainly the Binkhorst 2 loops model, but also posterior chamber lenses, and a few anterior chamber lenses. Indications and special cases are discussed, according to the type of cataract: senile, traumatic, combined cataract and glaucoma. Peroperative (intraocular lens-endothelium contact, vitreous loss) and postoperative complications (non-fixation of the lens, corneal bullous dystrophy, cortical material remmants, uveitis, cystoid macular oedema, retinal detachment) are described.