Objective. To improve prognostic ability in ankylosing spondylitis (AS), we sought to identify demographic, clinical, and immunogenetic characteristics associated with radiographic severity in a large cohort of patients. Methods. Patients with AS for >20 years were enrolled in a cross-sectional study (n ‫؍‬ 398). Pelvic and spinal radiographs were scored using the Bath Ankylosing Spondylitis Radiology Index for the spine (BASRI-s), and radiographic severity was measured as the BASRI-s/duration of AS. Clinical factors and HLA-B, DR, DQ, and DP alleles associated with the highest quartile of the distribution of radiographic severity were identified by first using random forests and then using multivariable logistic regression modeling. Similar procedures were used to identify factors associated with the lowest quartile of radiographic severity. Conclusion. The accuracy of the prognosis of radiographic severity in AS is improved by knowing the age at disease onset, sex, smoking history, and the presence of HLA-B*4100, DRB1*0804, DQA1*0401, DQB1*0603, DRB1*0801, and DPB1*0202 alleles. Results. Radiographic severity (being in the top quartile of BASRI-s/duration of AS) was associated with older age at onset of AS (odds ratio

Traveling wave tubes (TWTs) are vacuum electronic amplifiers (see Beck, Gittins, and Pierce) that are commonly used for communication in the centimeter wavelength range. Increasing demand for high data flow in wireless communication systems (satellite communication systems are a good example) raises needs for making TWT's more compact and efficient. Motivated by this we suggest a scheme in which a TWT with feedback is operated in a highly nonlinear regime where the device behaves chaotically. The chaos is controlled using small controls. Then, at the receiving end a receiving TWT synchronizes to the chaotic transmitter and amplifies the received signal with nearly no distortion. Results on numerical simulations of the proposed scheme are reported and used to evaluate its effectiveness.

We introduce a spatially localized inhomogeneity into the two-dimensional complex Ginzburg-Landau equation. We observe that this can produce two types of target wave patterns: stationary and breathing. In both cases, far from the target center, the field variables correspond to an outward propagating periodic traveling wave. In the breathing case, however, the region in the vicinity of the target center experiences a periodic temporal modulation at a frequency, in addition to that of the wave frequency of the faraway outward waves. Thus at a fixed point near the target, the breathing case yields a quasiperiodic time variation of the field. We investigate the transition between stationary and breathing targets, and note the existence of hysteresis. We also discuss the competition between the two types of target waves and spiral waves.

The effect of a long length scale static inhomogeneity on spiral wave dynamics is studied in the two-dimensional complex Ginzburg-Landau equation. We find that the inhomogeneity leads to the formation of a dominant spiral domain that suppresses other spiral domains, and that the spiral vortices slowly drift in the presence of an inhomogeneity with a velocity that is proportional to the local parameter gradients. We derive an expression for the spiral vortex drift velocity and present examples of both fixed point and limit cycle attractors of the spiral vortices.

The effect of weak inhomogeneity on spiral wave dynamics is studied within the framework of the two-dimensional complex Ginzburg-Landau equation description. The inhomogeneity gives spatial dependence to the frequency of spiral waves. This provides a mechanism for the formation of a dominant spiral domain that suppresses other spiral domains. The spiral vortices also slowly drift in the inhomogeneity, and results for the velocity are given. [S0031-9007(98)08283-0] PACS numbers: 82.40.Ck, 47.32.Cc, 47.54. + r Spiral waves occur in such diverse situations as cardiac arrythmias [1], reaction-diffusion systems (such as that describing the Belousov-Zhabotinsky reaction) [2,3], and slime mold colonies [4,5]. In this paper we consider the effect of an inhomogeneity of the supporting medium on spiral wave dynamics. For example, in the case of arrythmias, cardiac tissue is inherently inhomogeneous. For slime mold, an excitation inhomogeneity forms due to the sorting of the prestalk and prespore cells and the inhomogeneity results in spiral vortex motion [5]. As a potential example involving chemical reaction-diffusion systems, in Ref.[3] the chemical reaction rate was varied using its sensitivity to red laser light intensity. This could conveniently provide the means to create an inhomogeneity for a test of our theory by having the intensity vary over the entire system (other sources of reaction rate inhomogeneity are temperature inhomogeneity and inhomogeneity of the gel or porous glass medium in which chemical reaction-diffusion experiments are often done, etc.).We find that, for a weak inhomogeneity, the evolution proceeds on distinct time scales. In particular, we find that, after spirals first form, the inhomogeneity causes certain spirals that are favorably located in the inhomogeneous medium to widen their domains, crowding out and sweeping away less favorably located spirals. In addition, the spiral vortices slowly drift with a velocity linearly related to appropriate gradients of the background medium properties.Our studies of these effects are based on the twodimensional complex Ginzburg-Landau equation,where A͑x, y, t͒ is complex. This equation provides a universal description for extended media in which the homogeneous state is oscillatory and near a Hopf bifurcation [6]. The equation is obtained as a balance between weak growth ͓Re͑m͔͒, weak nonlinearity (jAj 2 A term), and weak spatial coupling (= 2 A term). In the case of a homogeneous medium a and b are real constants, and m can be set to unity by an appropriate rescaling of (1). A spiral wave solution to Eq. (1) then has the general form [7] A͑r, u, t͒ F͑r͒ exp͕i͓su 2 v o t 1 c͑r͔͖͒ . (2) The topological charge s 61 results in a 2ps phase increment of A for a counterclockwise circuit around the vortex center (r 0) where A 0. For large r, the solution (2) is locally a plane wave of wave number k o . Using the rescaling of m to unity, the frequency v o satisfies the dispersion relation v o a 1 ͑b 2 a͒k 2 o . The real functions F͑r͒ ϵ jAj and c͑r͒ have the f...