1,710 research outputs found
Every braid admits a short sigma-definite representative
A result by Dehornoy (1992) says that every nontrivial braid admits a
sigma-definite word representative, defined as a braid word in which the
generator sigma_i with maximal index i appears with exponents that are all
positive, or all negative. This is the ground result for ordering braids. In
this paper, we enhance this result and prove that every braid admits a
sigma-definite word representative that, in addition, is quasi-geodesic. This
establishes a longstanding conjecture. Our proof uses the dual braid monoid and
a new normal form called the rotating normal form
A divisibility result on combinatorics of generalized braids
For every finite Coxeter group , each positive braids in the
corresponding braid group admits a unique decomposition as a finite sequence of
elements of , the so-called Garside-normal form.The study of the
associated adjacency matrix allows to count the number of
Garside-normal form of a given length.In this paper we prove that the
characteristic polynomial of divides the one of . The
key point is the use of a Hopf algebra based on signed permutations. A similar
result was already known for the type . We observe that this does not hold
for type . The other Coxeter types (, , and ) are also studied.Comment: 28 page
Exploring the tree of numerical semigroups
In this paper we describe an algorithm visiting all numerical semigroups up
to a given genus using a well suited representation. The interest of this
algorithm is that it fits particularly well the architecture of modern
computers allowing very large optimizations: we obtain the number of numerical
semigroups of genus g 67 and we confirm the Wilf conjecture for g 60.Comment: 14 page
Geometrical analysis of thread milling – Part 1: Evaluation of tool angles
Thread milling is a method which is increasingly used for machining thread. For this operation, a helical interpolation is required. Furthermore, the thread mill is a tool whose geometry is rather complex. Its envelope profile is linked to the thread profile and a single tooth of the thread mill is composed of three continuous cutting edges. The present study proposes a geometrical model and an analytical formulation to define the rake face and the cutting edge. Further, the calculations of cutting planes and cutting angles are explained. The analysis shows specific aspects of thread mills, in particular the fact that the flute angle may lead to a negative rake angle. This study is a contribution to cutting geometry aspect and constitutes a step for cutting force model in thread milling
Investigation of tool geometry effect and penetration strategies on cutting forces during thread milling
The application of thread milling is increasing in industry because of its inherent advantages over other thread cutting techniques. The objective of this study is to investigate the effect of milling cutter tool geometry on cutting forces during thread milling. The proposed method can compare the performance of milling cutters in spite of the different number of tooth. The best thread milling cutter among the studied tools was determined from the cutting forces point of view. Furthermore, this study also pinpoints the best penetration strategy that provides minimum cutting forces. Lower cutting force variations will lead to fewer vibrations of the tool which in turn will produce accurate part.Postdoc de V Sharma financé par la région Bourgogn
Analysis and modeling of green wood milling: Chip production by slabber
During the primary transformation of wood, logs are faced with slabber heads. Chips produced are raw materials for pulp paper and particleboard industries. Efficiency of these industries is partly due to particle size distribution. Command of this distribution is no easy matter because of great dependence on cutting conditions and variability in material. This study aimed a better understanding and predictionof chip fragmentation. It starts with a detailed description of cutting kinematic and interaction between knife and log. This leads to the numerical development of a generic slabber head. Chip fragmentation phenomena were studied through experiments in dynamic conditions. These experiments were carried out thanks to a pendulum (Vc = 400 m/min). It was instrumented with piezoelectric force sensors and high speed camera. Obtained results agreed very well with previous quasi-static experiments
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