Business Employment Dynamics: Tabulations by Employer Size

The gross job gains and gross job loss statistics from the BLS Business Employment Dynamics (BED) program measure the large gross job flows that underlie the quarterly net change in employment. In the fourth quarter of 2004, employment grew by 869,000 jobs. This growth is the sum of 8.1 million gross job gains from opening and expanding establishments, and 7.2 million gross job losses from contracting and closing establishments. The new BED data have captured the attention of economists and policymakers across the country, and these data are becoming a major contributor to our understanding of employment growth and business cycles in the U.S. economy. Following the initial release of the BED data in September 2003, the BED data series expanded in May 2004 with the release of industry statistics. The BLS then began work on tabulations by size class. The production of size-class statistics is a complex task involving several economic and statistical issues. Although it is trivial to classify a business into a size class in any given quarter, it is difficult to classify a business into a size class for a longitudinal analysis of employment growth. Several different classifications exist, and many of these possible classifications have appealing theoretical and statistical properties. Furthermore, these alternative classification methodologies result in sharply different portraits of employment growth by size class. In this article, we discuss the alternative statistical methodologies that the BLS considered for creating size class tabulations from the Business Employment Dynamics data. Our primary focus is on four methodologies: quarterly base-sizing, annual base-sizing, mean-sizing, and dynamic-sizing. We discuss the evaluation criteria that BLS considered for choosing its official size class methodology.gross job gains; gross job losses; business employment dynamics; size-class statistics; dynamic-sizing

Micro-grippers for assembly of LIGA parts

This paper describes ongoing testing of two microgrippers for assembly of LIGA (Lithographie Galvanoformung Abformung) parts. The goal is to place 100 micron outside diameter (OD) LIGA gears with a 50 micron inner diameter hole onto pins ranging from 35 to 49 microns. The first micro gripper is a vacuum gripper made of a 100 micron OD stainless steel tube. The second micro gripper is a set of tweezers fabricated using the LIGA process. Nickel, Permalloy, and copper materials are tested. The tweezers are actuated by a collet mechanism which is closed by a DC linear motor

Miniature Autonomous Robotic Vehicle (MARV)

Sandia National Laboratories (SNL) has recently developed a 16 cm{sup 3} (1 in{sup 3}) autonomous robotic vehicle which is capable of tracking a single conducting wire carrying a 96 kHz signal. This vehicle was developed to assess the limiting factors in using commercial technology to build miniature autonomous vehicles. Particular attention was paid to the design of the control system to search out the wire, track it, and recover if the wire was lost. This paper describes the test vehicle and the control analysis. Presented in the paper are the vehicle model, control laws, a stability analysis, simulation studies and experimental results

Dynamics of a close-loop controlled MEMS resonator

The dynamics of a close-loop electrostatic MEMS resonator, proposed as a platform for ultra sensitive mass sensors, is investigated. The parameter space of the resonator actuation voltage is investigated to determine the optimal operating regions. Bifurcation diagrams of the resonator response are obtained at five different actuation voltage levels. The resonator exhibits bi-stability with two coexisting stable equilibrium points located inside a lower and an upper potential wells. Steady-state chaotic attractors develop inside each of the potential wells and around both wells. The optimal region in the parameter space for mass sensing purposes is determined. In that region, steady-state chaotic attractors develop and spend most of the time in the safe lower well while occasionally visiting the upper well. The robustness of the chaotic attractors in that region is demonstrated by studying their basins of attraction. Further, regions of large dynamic amplification are also identified in the parameter space. In these regions, the resonator can be used as an efficient long-stroke actuator