private boolean evaluateHeatClause(String str) {
		double x = parseMathExpression(str);
		if (Double.isNaN(x))
			return false;
		if (x == 0)
			return true;
		int n = model.getNumberOfParticles();
		if (n <= 0)
			return true;
		List<Particle> list = new ArrayList<Particle>();
		for (int k = 0; k < n; k++) {
			Particle p = model.getParticle(k);
			if (p.isSelected())
				list.add(p);
		}
		model.transferHeatToParticles(list, x);
		view.repaint();
		notifyChange();
		return true;
	}