Incidence density

Skin rashes are relatively common with flnoroqninolones. A retrospective cohort stndy in patients in general practice in the Netherlands focused on the nse of antibacterial agents and the occnrrence of adverse cntaneons events covered 469 505 consnltations with 87 475 patients, of whom 13 679 received prescriptions for antibiotics (57). After adjnstment for age, sex, and co-medications, the incidence density ratio (incidence density per 1000 exposed days) for varions gronps of antibacterial agents was as follows tetracyclines 1.0, macrohdes 1.1, flnoroqninolones 2.8, penicillins 2.9, and co-trimoxazole 4.4 (57). No details of the types of skin reactions were given, and it is therefore possible that phototoxic events were inclnded. Compared with other stndies, the reported rate of antibiotic-associated adverse cntaneons events in this ontpatient popnlation was rather low. 

Using the method of prescription event monitoring (PEM), the incidence densities of adverse effects per 1000 patient-months of exposure have been measured in 14 522 patients (2). Most were hypertensive (63%). During treatment months 2-6, the commonest adverse... 

A rate is an expression of the occurrence of an event. The time period must be specified and be identical for the numerator and denominator for the rate to be meaningful. Three kinds of rates are used in nosocomial infection surveillance incidence, prevalence, and incidence density. 

Incidence density is the instantaneous rate at which disease is occurring, relative to the size of the disease-free population. Incidence density is measured in units of the number of cases of disease per person per unit of time. An example of an incidence density that is commonly used in hospitals is the number of nosocomial pneumonias per 1000 ventilator-days. Incidence density is useful when the infection rate varies in a linear fashion to the length of time a patient is exposed to a risk factor (i.e., the longer the patient is exposed, the greater the chance of acquiring infection). For example ... 

Most of the published studies report the incidence rate of nosocomial pneumonia, that is, the number of cases of nosocomial pneumonia per 100 hospitalized patients. In six studies summarized in Table 3, the incidence of ventilator-associated pneumonia ranged from 9% to 24% (20). These rates fail to adjust for the duration of ventilation and are therefore difficult to interpret. Device-associated incidence density rates of nosocomial pneumonia, that is, the number of cases of ventilator-associated pneumonia per 1000 ventilator-days, are reported only for three studies and range from 10 to 30 per 1000 ventilator-days (14,21). In the NNIS, rates of ventilator-associated pneumonia per 1000 ventilator-days range from 9.4 in medical ICUs to 14.9 in surgical ICUs, 16.9 in trauma ICUs and 20.9 in burn ICUs. 

Incidence density rates of ventilator-associated pneumonia and nonventilator-associated pneumonia (reported by the NNIS system) from 1990 to 1996 are shown in Figure 2. On average, ventilator-associated pneumonia rates are 9.3 times higher than nonventilator-associated pneumonia rates, ranging from 2.6 times higher in respiratory ICUs to 19 times higher in burn ICUs. 

Table 1, Number of employee working hours, number injured, incidence density rates, rate ratios, 95% confidence intervals (CIs) and prevented fraction for back support use, Home Depot Stores, California 1989-94.

The physics of X-ray refraction are analogous to the well known refraction of light by optical lenses and prisms, governed by Snell s law. The special feature is the deflection at very small angles of few minutes of arc, as the refractive index of X-rays in matter is nearly one. Due to the density differences at inner surfaces most of the incident X-rays are deflected [1]. As the scattered intensity of refraction is proportional to the specific surface of a sample, a reference standard gives a quantitative measure for analytical determinations. 

Optical second-harmonic generation (SHG) has recently emerged as a powerful surface probe [95, 96]. Second harmonic generation has long been used to produce frequency doublers from noncentrosymmetric crystals. As a surface probe, SHG can be caused by the break in symmetry at the interface between two centrosymmetric media. A high-powered pulsed laser is focused at an angle of incidence from 30 to 70° onto the sample at a power density of 10 to 10 W/cm. The harmonic is observed in reflection or transmission at twice the incident frequency with a photomultiplier tube. 

The correlation fiinction G(/) quantifies the density fluctuations in a fluid. Characteristically, density fluctuations scatter light (or any radiation, like neutrons, with which they can couple). Then, if a radiation of wavelength X is incident on the fluid, the intensity of radiation scattered through an angle 0 is proportional to the structure factor... 

The oscillating electric dipole density, P (the polarization), that is induced by the total incident electric field,... 

The unique feature in spontaneous Raman spectroscopy (SR) is that field 2 is not an incident field but (at room temperature and at optical frequencies) it is resonantly drawn into action from the zero-point field of the ubiquitous blackbody (bb) radiation. Its active frequency is spontaneously selected (from the infinite colours available in the blackbody) by the resonance with the Raman transition at co - 0I2 r material. The effective bb field mtensity may be obtained from its energy density per unit circular frequency, the... 

We have thus far discussed the diffraction patterns produced by x-rays, neutrons and electrons incident on materials of various kinds. The experimentally interesting problem is, of course, the inverse one given an observed diffraction pattern, what can we infer about the stmctirre of the object that produced it Diffraction patterns depend on the Fourier transfonn of a density distribution, but computing the inverse Fourier transfomi in order to detemiine the density distribution is difficult for two reasons. First, as can be seen from equation (B 1.8.1), the Fourier transfonn is... 

Let the rate of the event under study be R. It will be proportional to the cross section for the process under study, a, the incident electron current, Iq, the target density, n, the length of the target viewed by the detectors,, the solid angles subtended by the detectors, Aoi and A012 the efficiency of the detectors, and... 

Figure Bl.10.10. Schematic diagram of the effect of detector view angles on coincidence rate. The view angles of two detectors are shown along with the common view angle. Maximum signal collection efficiency is achieved when the individual view angles have the maximum overlap and when the overlap coincides with the maximum density of the incident beam.

A unifonn monoenergetic beam of test or projectile particles A with nnmber density and velocity is incident on a single field or target particle B of velocity Vg. The direction of the relative velocity m = v -Vg is along the Z-axis of a Cartesian TTZ frame of reference. The incident current (or intensity) is then = A v, which is tire number of test particles crossing unit area nonnal to the beam in unit time. The differential cross section for scattering of the test particles into unit solid angle dO = d(cos vji) d( ) abont the direction ( )) of the final relative motion is... 

This relation is a direct consequence of the conservation of flux. The target casts a shadow in the forward direction where the intensity of the incident beam becomes reduced by just that amount which appears in the scattered wave. This decrease in intensity or shadow results from interference between the incident wave and the scattered wave in the forward direction. Figure B2.2.2 for the density P (r) of section B2.2.6 illustrates... 

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