On the axioms for adhesive and quasiadhesive categories

A category is adhesive if it has all pullbacks, all pushouts along monomorphisms, and all exactness conditions between pullbacks and pushouts along monomorphisms which hold in a topos. This condition can be modified by considering only pushouts along regular monomorphisms, or by asking only for the exactness conditions which hold in a quasitopos. We prove four characterization theorems dealing with adhesive categories and their variants.Comment: 20 pages; v2 final version, contains more details in some proof

Palinspastic reconstruction of southeastern California and southwestern Arizona for the middle Miocene

A paleogeographic reconstruction of southeastern California and southwestern Arizona at 10 Ma was made based on available geologic and geophysical data. Clockwise rotation of 39 deg was reconstructed in the eastern Transverse Ranges, consistent with paleomagnetic data from late Miocene volcanic rocks, and with slip estimates for left-lateral faults within the eastern Transverse Ranges and NW-trending right lateral faults in the Mojave Desert. This domain of rotated rocks is bounded by the Pinto Mountain fault on the north. In the absence of evidence for rotation of the San Bernardino Mountains or for significant right slip faults within the San Bernardino Mountains, the model requires that the late Miocene Pinto Mountain fault become a thrust fault gaining displacement to the west. The Squaw Peak thrust system of Meisling and Weldon may be a western continuation of this fault system. The Sheep Hole fault bounds the rotating domain on the east. East of this fault an array of NW-trending right slip faults and south-trending extensional transfer zones has produced a basin and range physiography while accumulating up to 14 km of right slip. This maximum is significantly less than the 37.5 km of right slip required in this region by a recent reconstruction of the central Mojave Desert. Geologic relations along the southern boundary of the rotating domain are poorly known, but this boundary is interpreted to involve a series of curved strike slip faults and non-coaxial extension, bounded on the southeast by the Mammoth Wash and related faults in the eastern Chocolate Mountains. Available constraints on timing suggest that Quaternary movement on the Pinto Mountain and nearby faults is unrelated to the rotation of the eastern Transverse Ranges, and was preceded by a hiatus during part of Pliocene time which followed the deformation producing the rotation. The reconstructed Clemens Well fault in the Orocopia Mountains, proposed as a major early Miocene strand of the San Andreas fault, projects eastward towards Arizona, where early Miocene rocks and structures are continuous across its trace. The model predicts a 14 deg clockwise rotation and 55 km extension along the present trace of the San Andreas fault during late Miocene and early Pliocene time. Palinspastic reconstructions of the San Andreas system based on this proposed reconstruction may be significantly modified from current models

Combatting Unemployment: Is Flexibility Enough?

Our conclusions are the most important influences on unemployment come from the following (i) The longer unemployment benefits are available the longer unemployment lasts. Similarly, higher levels of benefits generate higher unemployment, with an elasticity of around one half. On the other hand active help in finding work can reduce unemployment. So more "flexibility" may need to be complemented by more intervention to provide active help. (ii) Union coverage and union power raise unemployment. But if wage bargaining is decentralised, wage bargainers have incentives to settle for more than the "going-rate", and only higher unemployment can prevent them leap-frogging. Although decentralisation makes it easier to vary relative wages, this advantage is more than offset by the extra upward pressure on the general level of wages. Thus, where union coverage is high, coordinated wage bargaining leads to lower unemployment. (iii) Conscious intervention to raise the skill levels of less able workers is an important component of any policy to combat unemployment. Pure wage flexibility may not be sufficient because it leads to growing inequality which in turn discourages labour supply from less able workers. Thus in these areas it is clear what types of reforms are needed. If well designed, such reforms might halve the level of unemployment in many countries. But there are three remedies which have been widely advocated in both OECD Jobs Study and the Delors White Paper. These are: less employment protection, lower taxes on employment, and lower working hours. Our research does not suggest that lower employment taxes or lower hours would have any long term effects; while the effects of lower employment protection would be small. (iv) Lower employment protection has two effects. It increases hiring and thus reduces long-term unemployment. But it also increases firing and thus increases short-term unemployment. The first (good) effect is almost offset by the second (bad) one. The gains from flexibility are small. (v) Employment taxes do not appear to have any long-term effect on unemployment and are borne entirely by labour. There may be some short-term effects, but it is not clear that there would be any fall in inflationary pressure if taxes on polluting products were raised at the same time as taxes on employment were lowered. (vi) Hours of work appear to have no long-term effect upon employment. Equally, if early retirement is used in order to reduce labour supply, it is necessary to reduce employment pari passu unless inflationary pressure is to increase. While flexibility hours and participation can reduce the fluctuations in unemployment over the cycle, they cannot affect its average level.