Matthew Davidson

Presentism and the non-present

In this paper I argue that presentism has a problem accounting forthe truth of statements whose truth conditions seem to require therebe relations that hold between present and non-present objects. Imotivate the problem and then examine several strategies for dealingwith the problem. I argue that no solution is forthcoming, and thispresents a prima facie problem for presentism.

Knowledge and reality

objects. What might the nominalist say in reply? The most plausible reply open to the nominalist seems to me to be along the following lines. My platonist critic is certainly a very literal-minded fellow. I didn’t mean the ‘some’ in the open sentence ‘x is like y in some anatomically relevant ways’ to be taken as a quantifier: I didn’t mean this sentence to be read ‘∃z (z is a way in which a thing can be like a thing and z is anatomical and x is like y in z)’. That’s absurd. One might as well read ‘There’s more than one way to skin a cat’ as ‘∃x ∃y (x is a way of skinning a cat and y is a way of skinning a cat and x y)’. I meant this open sentence to have no internal logical structure, or none beyond that implied by the statement that two variables are free in it. It’s just a form of words we learn to use by comparing various pairs of objects in the ordinary business of life. And here is the rejoinder to this reply: If you take that line you confront problems it would be better not to have to confront. Consider the sentence ‘x is like y in some physiologically relevant ways’. Surely there is some logical or structural or syntactical 20 Peter van Inwagen relation between this sentence and ‘x is like y in some anatomically relevant ways’? One way to explain the relation between these two sentences is to read the former as ‘∃z (z is a way in which a thing can be like a thing and z is physiological and x is like y in z)’ and the latter as ‘∃z (z is a way in which a thing can be like a thing and z is anatomical and x is like y in z)’. How would you explain it? Or how would you explain the relation between the sentences ‘x is like y in some anatomically relevant ways’ (which you say has no logical structure) and ‘x is like y in all anatomically relevant ways’? If neither of these sentences has a logical structure, how do you account for the obvious validity of the argument Either of two female spiders of the same species is like the other in all anatomically relevant ways. Hence, an insect that is like a given female spider in some anatomically relevant ways is like any female spider of the same species in some anatomically relevant ways? If the premise and conclusion of this argument are read as having the logical structure their syntax suggests, the validity of this argument is easily demonstrable in textbook quantifier logic. If one insists that they have no logical structure, one will find it difficult to account for the validity of this argument. That is one of those problems I alluded to, one of those problems it would be better not to have to confront. (One of thousands of such problems.) I suggest that we can learn a lesson from this little exchange between an imaginary nominalist and an imaginary platonist: that one should accept the following condition of adequacy on philosophical paraphrases. Paraphrases must not be such as to leave us without an account of the logical relations between predicates that are obviously logically related. Essentially the same constraint on paraphrase can be put in these words: A paraphrase must not leave us without an account of the validity of any obviously valid argument. Accepting this constraint has, I believe, a significant consequence. This consequence requires a rather lengthy statement. Apparent quantification over properties pervades our discourse. In the end, one can avoid quantifying over properties only by quantifying over other sorts of abstract object—”ways in which a thing can be like a thing,” for example. But most philosophers, if forced to chose between quantifying over properties and quantifying over these other objects

Magneto-optical imaging study of the crack formation in superconducting tapes caused by applied strain

The crack formation in filaments of multi-filamentary Bi2Sr2Ca2Cu3Ox tapes as function of applied longitudinal strain is visualized by means of magneto-optical imaging. Strain is applied at the desired temperature inside a helium flow cryostat. Cracks form transverse to the current carrying direction of the filaments. Before the tape breaks entirely, all filaments have formed a large number of transverse cracks, spaced with an average crack distance of ≈200 μm. The crack formation is compared with the degradation of the critical current as a function of the applied strain. The critical current degrades already before the first crack is observed. This is explained by the limited number of filaments visible in the experiment.

Two- and three-dimensional connectivity and current distribution in YBa2Cu3Ox-coated conductors

The microstructure of YBa2Cu3Ox sYBCOd-coated conductors depends strongly on the deposition method and thickness of the YBCO layer. This letter shows how the clear qualitative difference in grain connectivity between vacuum-deposited and solution-grown layers has direct consequences for the spatial distribution of the critical current density sJcd. Pulsed-laser-deposited YBCO conductors usually have a columnar grain structure that results in a two-dimensional current network, as demonstrated with magneto-optical imaging. Consequently, their transport Jc varies considerably on length scales from 50 mm up to 5 mm, with current suppression occurring even at defects that run parallel to the macroscopic current. In contrast, the thicker YBCO coatings in metalorganic-deposited samples have a layered structure, leading to a three-dimensional current path. Magneto-optically, this is deduced from sample-wide shielding currents, while transport experiments reveal much smaller spatial variations in Jc. These results are encouraging for the further development of nonvacuum produced YBCO-coated conductors, since such three-dimensional systems are inherently more “forgiving” of local defects.

Direct experimental analysis of the relation between the grain structure and the distribution of critical current density in YBa2Cu3Ox coated conductors

We present a relatively simple experimental method to correlate the grain structure of YBa2Cu3Ox coated conductors with spatial variations of the critical current density on a macroscopic scale. Variations of the current density on a micrometre scale are visualized with magneto-optical imaging, using the flux trapped by colonies of grains to quantify the degree of connectivity. Integrating these trapped flux profiles over larger distances yields direct information of the critical current distribution on a millimetre scale, provided that contributions from negative return flux in colony boundaries are properly eliminated. Flux polarity is determined using the wavelength dependence of the Verdet constant. The validity of this analysis is demonstrated by comparing the results with direct transport data on the lateral current distribution, measured with the magnetic knife technique. The combination of both experiments shows that the critical current density is suppressed over several millimetres of conductor length at areas where a large number of high-angle grain boundaries or defects are present.

A demonstration against theistic activism

Many theists have tried to work out coherent accounts of the relationship between God and abstract objects. Some have contended that abstracta depend on God for their existence and nature. Following Christopher Menzel and Thomas Morris, I call such a position, theistic activism. In this essay, I begin by examining some motivations for holding such a position. Then, I try to make sense of how objects might depend on God. Finally, I object to theistic activism on the grounds that one who holds to it is committed to the claim that God causes himself to exist and causes himself to have such properties as omnipotence and omniscience.