torch.Tensor(10) will return an uninitialized FloatTensor with 10 values, while torch.tensor(10) will return a LongTensor containing a single value (10).
I would recommend to use the second approach (lowercase t) or any other factory method instead of creating uninitialized tensors via torch.Tensor or torch.FloatTensor.
To explicitly create a tensor with uninitialized memory, you could still use torch.empty.